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                                                                     EXHIBIT 5.1
                                LATHAM & WATKINS
                                Attorneys at Law
                       633 West Fifth Street, Suite 4000
                       Los Angeles, California 90071-2007
                            Telephone (213) 485-1234
                               Fax (213) 891-8763
 
                                 April 16, 1998
 
Beckman Coulter, Inc.
2500 Harbor Boulevard
Fullerton, CA 92834
 
     Re: Beckman Coulter, Inc.
       Registration Statement on Form S-4 (File No. 333-          )
 
Ladies and Gentlemen:
 
     At your request, we have examined the Registration Statement on Form S-4
(the "Registration Statement") referenced above, which you are filing on the
date hereof with the Securities and Exchange Commission in connection with the
registration under the Securities Act of 1933, as amended, of (i) $160,000,000
principal amount of your 7.10% Senior Notes due 2003 and (ii) $240,000,000
principal amount of your 7.45% Senior Notes due 2008 (together, the "Exchange
Notes"), to be offered and issued by Beckman Coulter, Inc. (the "Company"),
together with guarantees of the Exchange Notes (the "Guarantees") by Beckman
Instruments (Naguabo) Inc., a California corporation, Hybritech Incorporated, a
California corporation, SmithKline Diagnostics, Inc., a Delaware corporation and
Coulter Corporation, a Delaware corporation (collectively, the "Guarantors")
pursuant to an Indenture dated March 4, 1998 (the "Indenture") among the
Company, the Guarantors and The First National Bank of Chicago, as trustee.
 
     As such counsel, we have made such legal and factual examinations and
inquiries as we have deemed necessary or appropriate for purposes of this
opinion. In our examination, we have assumed the genuineness of all signatures,
the authenticity of all documents submitted to us as originals, and the
conformity to authentic original documents of all documents submitted to us as
copies. As to facts material to the opinions, statements and assumptions
expressed herein, we have, with your consent, relied upon oral or written
statements and representations of officers and other representatives of the
Company, the Guarantors and others. In addition, we have obtained and relied
upon such certificates and assurances from public officials as we have deemed
necessary.
 
     We are opining herein as to the effect on the subject transaction only of
the internal laws of the State of New York and the California Corporations Code
and the General Corporation Law of the State of Delaware, and we express no
opinion with respect to the applicability thereto, or the effect thereon, of any
other laws.
 
     Based upon the foregoing, we are of the opinion that, upon issuance thereof
in the manner described in the Registration Statement, the Exchange Notes will
be legally valid and binding obligations of the Company and the Guarantees will
be legally valid and binding obligations of the respective Guarantors.
 
     The opinion rendered above is subject to the following exceptions,
limitations and qualifications: (i) the effect of bankruptcy, insolvency,
reorganization, moratorium or other similar laws now or hereafter in effect
relating to or affecting the rights and remedies of creditors; (ii) the effect
of general principles of equity, whether enforcement is considered in a
proceeding in equity or at law, and the discretion of the court before which any
proceeding therefor may be brought; (iii) the unenforceability under certain
circumstances under law or court decisions of provisions providing for the
indemnification of or contribution to a party with respect to a liability where
such indemnification or contribution is contrary to public policy; and (iv) we
express no opinion concerning the enforceability of the waiver of rights or
defenses contained in Section 515 of the Indenture.
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Beckman Coulter, Inc.
April 16, 1998
Page 2
 
     This opinion is rendered only to you and is solely for your benefit in
connection with the transactions covered hereby. This opinion may not be relied
upon by you for any other purpose, or furnished to, quoted to, or relied upon by
any other person, firm or corporation for any purpose, without our prior written
consent.
 
     We consent to your filing this opinion as an exhibit to the Registration
Statement.
 
                                          Very truly yours,
 
                                          LATHAM & WATKINS