EXHIBIT 5.1



                                 August 24, 2001

CNS, Inc.
PO Box 39802
Minneapolis, MN 55439

RE:      OPINION OF COUNSEL AS TO LEGALITY OF 200,000 SHARES OF COMMON STOCK TO
         BE REGISTERED UNDER THE SECURITIES ACT OF 1933

Ladies and Gentlemen:

         This opinion is furnished in connection with the registration under the
Securities Act of 1933 on Form S-8 of 200,000 shares of Common Stock, $.01 par
value per share, of CNS, Inc., (the "Company") offered to employees of the
Company or its subsidiaries pursuant to the CNS, Inc. 1989 Employee Stock
Purchase Plan (the "Plan").

         As general counsel for the Company, we advise you that it is our
opinion, based on our familiarity with the affairs of the Company and upon our
examination of pertinent documents, that the 200,000 shares of Common Stock to
be offered to employees under the Plan will, when paid for and issued, be
validly issued and lawfully outstanding, fully paid and nonassessable shares of
Common Stock of the Company.

         The undersigned hereby consent to the filing of this opinion with the
Securities and Exchange Commission as an Exhibit to the Registration Statement
with respect to said shares of Common Stock under the Securities Act of 1933.

                                                 Very truly yours,

                                                 LINDQUIST & VENNUM P.L.L.P.

                                                 /s/ Lindquist & Vennum P.L.L.P.