Exhibit 4.6

Commerce Bank
Post Office Box 419248
Kansas City, Missouri 64141-6428
(816) 234-2000


May 12, 1999



Mr. Steven K. Fitzwater
Executive Vice President,
 Chief Operating Officer and Secretary
LAB HOLDINGS, INC.
5000 W. 95th Street, Suite 260
Shawnee Mission, Kansas  66207


Re:  Line of Credit


Dear Mr. Fitzwater:

I am pleased to advise you that the Senior Loan Committee of Commerce Bank, N.A.
("Bank")  has  approved an  unsecured  line of credit in the  maximum  principal
amount of  $15,000,000  ("Line of Credit") to Lab  Holdings,  Inc.  ("Company").
Additional  terms for the Line of Credit  (which shall survive the execution and
delivery of the Line of Credit Note [hereinafter  described] and shall not merge
therewith) are as follows:

PURPOSE:  The proceeds of the Line of Credit shall be used by Company to finance
the day to day operations  of  its  subsidiary,  LabOne, Inc. ("LabOne") and  to
finance Company's repurchase of LabOne stock.

INTEREST:  Each  borrowing  under the Line of Credit  shall  bear  interest,  at
Company's  option to be selected at the time of each borrowing,  at either (i) a
variable  per annum rate equal to the Prime Rate,  or (ii) a variable  per annum
rate  equal to  three-quarters  of one  percent  (.75%) in excess of the  "LIBOR
Rate".  For purposes  hereof,  (i) "Prime Rate" shall mean the per annum rate of
interest  established from time to time by Bank for its own internal convenience
as its Prime Rate,  which when used to compute  the rate of  interest  hereunder
shall change as of the date of any change in said Prime Rate; no  representation
is made that the Prime Rate is the best, lowest or favored rate of interest, and
(ii) "LIBOR Rate" shall mean the thirty-day  London  Interbank  Offered Rate, as
quoted in the Money Rates section of The Wall Street Journal,  the Knight-Ridder
News Service, or such



Mr. Steven K. Fitzwater
May 12, 1999
Page 2

other news service used by Bank, on the business day  immediately  preceding the
date of the applicable borrowing (or the business day immediately  preceding the
date of any adjustment  date, as applicable);  the LIBOR Rate, with respect to a
particular  borrowing,  shall be subject to  adjustment  every thirty days based
upon the then  applicable  LIBOR Rate.  Interest on the Line of Credit  shall be
calculated  on the  actual  number  of days  outstanding  on the basis of a year
consisting of 360 days and shall be payable monthly, in arrears.

REPAYMENT, MATURITY: Principal under the Line of Credit shall be due and payable
in full on October 31,  2000;  until such date,  Company  may borrow,  repay and
reborrow such sums as Company  desires in its sole discretion (but not to exceed
the maximum principal amount, at any time outstanding, of $15,000,000).

PROMISSORY NOTE: The Line of Credit shall be evidenced by a Line of Credit Note,
dated the closing date of the Line of Credit,  in form and substance  acceptable
to Bank.

COMMITMENT FEE: For the commitment of Bank contained  herein,  Company agrees to
pay Bank a per annum  commitment  fee equal to one-tenth of one percent (.1%) of
the  average  unused  amount of the Line of  Credit.  Such fee shall be  payable
quarterly, in arrears. Company shall have the option, at any time, and from time
to time,  to  irrevocably  reduce  the  amount of Bank's  commitment  hereunder;
provided, however, in any event Company shall pay to Bank a per annum commitment
fee of at least $10,000.

TERM LOAN CONVERSION OPTIONS:  Company shall have the option, from time to time,
to request that the outstanding  principal  balance (or a portion thereof) under
the Line of Credit be converted to a term loan (with a  corresponding  reduction
in the  amount of Bank's  commitment  under  the Line of  Credit),  on terms and
conditions satisfactory to Bank in its sole discretion.

REPRESENTATIONS:  Company  represents and warrants to Bank that the Company is a
corporation  existing  and in good  standing  under  the  laws of the  State  of
Missouri;  that  the  Company  has  corporate  power  and  authority  to own its
properties  and to enter into this  agreement,  borrow  monies from the Bank and
perform  its  obligations   hereunder,   and  that  such  entry,  borrowing  and
performance  has been  authorized  by all  necessary  corporate  action  and has
received all  necessary  governmental  approval  (if any shall be required)  and
shall not  contravene or conflict with any provision of law or of the charter or
by-laws  of the  Company  or of any  agreement,  law or order  binding  upon the
Company; that all



Mr. Steven K. Fitzwater
May 12, 1999
Page 3

financial  statements  delivered to the Bank on behalf of the Company accurately
present the financial condition of the Company;  that since the date of the last
financial  statements of the Company  delivered to the Bank, no material adverse
change in the  business,  assets,  operations  or  prospects of the Company have
occurred of which the Bank has not been advised  either  verbally or in writing;
and that no litigation  or other  contingent  liability  exists which may have a
material adverse effect on the business,  assets, operations or prospects of the
Company of which the Bank has not been advised in writing. Furthermore,  Company
represents  and warrants that all software  utilized in the conduct of Company's
business will have appropriate  capabilities and  compatibility for operation to
handle  calendar dates falling on or after January 1, 2000, and all  information
pertaining  to such  calendar  dates,  in the  same  manner  and  with  the same
functionality  as the software  does  respecting  calendar  dates  falling on or
before December 31, 1999. Additionally, Company represents and warrants that the
data-related user interface  functions,  data-fields,  and data-related  program
instructions and functions of the subject software include the indication of the
century.  The representations and warranties contained herein shall be deemed to
be continuing while this commitment letter remains in effect and/or any sums are
outstanding under the Line of Credit Note.

FINANCIAL INFORMATION:  The Company shall deliver to the Bank the following
information:

         (a)  Within  one  hundred  twenty-five  (125)  days  after  its  fiscal
year-end,  the  audited  year-end  financial  statements  of  Company,  in  form
acceptable  to Bank and prepared by  independent  certified  public  accountants
acceptable to Bank;

         (b) Within fifty (50) days after the end of each  quarter,  the balance
sheets  and profit and loss  statements  of Company  dated as of the end of such
quarter, certified by the Chief Financial Officer of Company;

         (c)  Within  one  hundred  twenty-five  (125)  days  after  its  fiscal
year-end,   the  audited  year-end  financial  statements  of  LabOne,  in  form
acceptable  to Bank and prepared by  independent  certified  public  accountants
acceptable to Bank;

         (d) Within fifty (50) days after the end of each  quarter,  the balance
sheets  and  profit and loss  statements  of LabOne  dated as of the end of such
quarter, certified by the Chief Financial Officer of LabOne; and




Mr. Steven K. Fitzwater
May 12, 1999
Page 4

         (e) From  time to  time,  such  additional  information  regarding  the
respective financial positions,  conditions or businesses of Company and LabOne,
as the Bank may reasonably request.

COVENANTS:  For such period of time as this commitment letter remains in effect,
or any  indebtedness  owing  hereunder  or under the Line of Credit Note remains
unpaid, Company covenants and agrees:

         (a) Company shall permit Bank, and any person designated by Bank as its
agent,  to inspect and review any of  Company's  properties,  assets,  corporate
books and financial records,  and to discuss its affairs,  finances and accounts
with its principal officers and independent certified public accountants, all at
such reasonable times and as often as Bank may reasonably request;

         (b) Company shall:  pay and discharge  prior to delinquency  all debts,
accounts,  liabilities,  assessments, and governmental charges or levies imposed
upon it or upon its income or profits or upon any of its  properties  (provided,
however,  Company  shall  not be  required  to pay  any  taxes,  assessments  or
governmental  charges  being  diligently  contested  by  it  in  good  faith  by
appropriate legal proceedings);  do all things necessary to preserve and keep in
full  force  and  effect  its  corporate  existence,   rights,   franchises  and
privileges; and comply with all applicable statutes,  regulations and orders of,
and all applicable  restrictions  imposed by, any  governmental  authority,  the
noncompliance  with which  could  materially  adversely  affect its  business or
credit;

         (c) Company shall notify Bank in writing of any default  hereunder,  or
under any indenture,  agreement,  contract or other  instrument to which it is a
party  or by  which it is  bound,  or of any  acceleration  of  maturity  of any
indebtedness  owing by it,  and shall take all such  steps as are  necessary  or
appropriate to promptly remedy any such default;

         (d) Except with respect to a merger involving LabOne, Company shall not
merge or consolidate with another entity or sell all or substantially all of its
assets to any person, firm or corporation; and

         (e)  There  shall  be no  material  adverse  change  in  the  financial
condition of Company or the nature of its business.



Mr. Steven K. Fitzwater
May 12, 1999
Page 5

EVENTS  OF  DEFAULT:  Upon the  occurrence  of any of the  following  events  of
default:  failure of Company to comply with any of the  provisions  contained in
this commitment  letter or in any other agreement  between Company and Bank; any
event under any other agreement to which Company is a party which allows Bank or
any other party to declare any indebtedness  owing by Company due and payable in
full; or  dissolution,  termination of existence,  insolvency,  appointment of a
receiver  of any part of the  property  of, an  assignment  for the  benefit  of
creditors, or the commencement of any proceedings under bankruptcy of insolvency
laws by or against Company;  then or at any time thereafter,  all obligations of
Company owing to Bank, shall  immediately  become due and payable without notice
or demand.  Unless  prohibited  by law,  Company will pay on demand all costs of
collection,  legal expenses and  attorneys'  fees incurred or paid in collecting
and/or enforcing this commitment letter and/or the Line of Credit.  Furthermore,
Bank reserves the right to offset  without notice all funds held by Bank against
matured debts owing to Bank by Company.

MISCELLANEOUS:

         (a) This  commitment  letter  shall be governed  by, and  construed  in
accordance with, the laws of the State of Missouri.

         (b) ORAL  AGREEMENTS OR COMMITMENTS TO LOAN MONEY,  EXTEND CREDIT OR TO
FORBEAR  FROM  ENFORCING  REPAYMENT OF A DEBT,  INCLUDING  PROMISES TO EXTEND OR
RENEW  SUCH  DEBT,  ARE  NOT  ENFORCEABLE.  TO  PROTECT  YOU  (BORROWER)  AND US
(CREDITOR)  FROM  MISUNDERSTANDING  OR  DISAPPOINTMENT,  ANY AGREEMENTS WE REACH
COVERING SUCH MATTERS ARE  CONTAINED IN THIS WRITING,  WHICH IS THE COMPLETE AND
EXCLUSIVE STATEMENT OF THE AGREEMENT BETWEEN US, EXCEPT AS WE MAY LATER AGREE IN
WRITING TO MODIFY IT.

         BY  SIGNING  BELOW,  YOU AND WE AGREE THAT THERE ARE  NO UNWRITTEN ORAL
 AGREEMENTS BETWEEN US.

If the terms and conditions contained in this commitment letter are satisfactory
to you, please sign and return the enclosed duplicate of this commitment letter.
Upon the Bank's receipt of the signed  duplicate,  this commitment  letter shall
become the controlling  agreement,  with respect to the Line of Credit,  between
Commerce Bank, N.A. and Lab Holdings,  Inc. If not accepted and returned to Bank
by May 31, 1999 (or such later date as Bank shall agree upon in  writing),  this
commitment shall automatically expire.




Mr. Steven K. Fitzwater
May 12, 1999
Page 6

If you have any  questions  regarding  this  commitment  letter  or any  matters
relating to this  financing,  please do not hesitate to call me.  Commerce  Bank
sincerely  appreciates  this  opportunity  and looks forward to  continuing  its
relationship with Lab Holdings, Inc.

Sincerely,



s/Pam Hill
Pamela T. Hill
Vice President

cc:      Mr. Robert D. Thompson
         Executive Vice President
          and Chief Operating Officer
         LabOne, Inc.


Acknowledged and accepted this 14 day of May, 1999.


LAB HOLDINGS, INC.



By:s/Steven K. Fitzwater
   Steven K. Fitzwater

Title: EVP, COO, CFO & Secretary























                               LINE OF CREDIT NOTE


$15,000,000                                              May 14 , 1999
Maximum Amount and Interest                              Kansas City, Missouri


         FOR VALUE RECEIVED, the undersigned,  LAB HOLDINGS, INC. ("Company"), a
Missouri corporation, hereby promises to pay to the order of COMMERCE BANK, N.A.
("Bank")  the  principal  sum  of the  lesser  of (a)  FIFTEEN  MILLION  DOLLARS
($15,000,000) and (b) the aggregate unpaid principal amount of all advances made
by the Bank to Company  pursuant to the Letter  Agreement,  dated May 12,  1999,
between the Bank and Company.  Principal under this Line of Credit Note shall be
due and  payable in full on October  31,  2000;  until  such date,  Company  may
borrow,  repay and reborrow such sums as Company  desires in its sole discretion
(but not to exceed the maximum principal  amount,  at any time  outstanding,  of
$15,000,000).  Company  agrees to pay  interest on the unpaid  principal  amount
hereof from time to time from the date hereof until such amount shall become due
and payable  (whether at the stated  maturity,  by acceleration or otherwise) at
the  interest  rate  determined  in  accordance  with the  terms  of the  Letter
Agreement.  Interest shall be payable monthly, in arrears, and upon the due date
and  payment  (including  prepayment)  in full of the  unpaid  principal  amount
hereof.  The  principal  balance of this Line of Credit Note shall bear interest
after maturity,  whether by acceleration or otherwise,  at the per annum rate of
three  percent  (3%) in excess  of the  Prime  Rate (as  defined  in the  Letter
Agreement),  but not to exceed the maximum  rate allowed by law; and if not paid
monthly,  such interest shall be compounded monthly. Both principal and interest
shall be payable in lawful money of the United  States of America to Bank at its
office at 1000 Walnut  Street,  Kansas  City,  Missouri  64106,  in  immediately
available funds.

         Bank is authorized to endorse on the schedule annexed hereto and made a
part hereof,  or on a continuation  thereof,  or to otherwise record in a manner
satisfactory to the Bank,  appropriate  notations evidencing the date and amount
of each advance,  the interest  rate(s) with respect  thereto,  and the date and
amount of each payment,  which  endorsement or recording shall  constitute prima
facie evidence of the accuracy of the




information endorsed or recorded;  provided,  however,  that the failure to make
such notations or recordings  shall not affect the  obligations of Company under
this Line of Credit Note or the Letter  Agreement  or affect the validity of any
payment with respect thereto.

         If any  payment  under this Line of Credit  Note  shall  become due and
payable on a day which is not a business day of Bank,  payment  shall be made on
the next  succeeding  business day and,  with respect to payments of  principal,
interest shall be payable thereon at the applicable rate during such extension.

         Unless  prohibited  by law,  Company will pay on demand all  reasonable
costs of  collection,  legal  expenses and  attorneys'  fees incurred or paid in
collecting and/or enforcing this Line of Credit Note. Furthermore, Bank reserves
the right to offset  without  notice all funds of Company  held by Bank  against
matured debts owing to Bank by Company.

         All without  notice and without  affecting its liability to Bank,  each
guarantor,  endorser or accommodation  maker: (1) waives  presentment,  protest,
demand,  notice of dishonor or default, and consents to the release of any party
or parties  directly or  indirectly  liable for payment  hereof or the  release,
subordination or substitution of any collateral  securing this  obligation;  and
(2) consents to any and all amendments and modifications  (including  changes in
interest rate).

         This Line of Credit Note is the "Line of Credit Note"  issued  pursuant
to the provisions of the Letter Agreement,  to which Letter Agreement, as it may
be amended  from time to time,  reference  is hereby made for a statement of the
terms and conditions  under which this Line of Credit Note may be prepaid or its
maturity  accelerated.  Reference  is hereby made to such Letter  Agreement  for
additional duties and obligations to be performed by Company, and for additional
rights and interests in favor of Bank.

         This Line of  Credit  Note  shall be  governed  by,  and  construed  in
accordance with, the laws of the State of Missouri.





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         IN WITNESS WHEREOF, Company has duly caused this Line of Credit Note to
be executed and delivered at the place  specified above and as of the date first
written above.

                                               LAB HOLDINGS, INC.



                                               s/Steven K. Fitzwater
                                               By: Steven K. Fitzwater
                                               Title: EVP, COO, CFO & Secretary

































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