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                                                                      EXHIBIT 5
 
                                                              February 14, 1997
 
Commerce Bancshares, Inc.
1000 Walnut, 18th Floor
Kansas City, MO 64106
 
Ladies and Gentlemen:
 
  We have acted as counsel to Commerce Bancshares, Inc., a Missouri
corporation ("Commerce"), in connection with the transactions contemplated by
the Agreement and Plan of Reorganization, dated as of January 16, 1997 (the
"Acquisition Agreement"), by and among Commerce, CBI-Kansas, Inc. ("CBI"),
Shawnee Bancshares, Inc. ("Shawnee") and The Shawnee State Bank (the "Bank").
 
  This opinion is being furnished in accordance with the requirements of Item
601(b)(5) of Regulation S-K under the Securities Act of 1933, as amended (the
"Securities Act").
 
  Pursuant to the Acquisition Agreement, Shawnee will be merged with and into
CBI, with CBI being the surviving corporation (the "Merger"). In the Merger,
the outstanding shares of common stock, $1.00 par value, and preferred stock,
$55 par value, of Shawnee, other than any shares owned by Commerce, CBI,
Shawnee or any of their (which shares will be canceled), will be exchanged for
fully paid and nonassessable shares of common stock, $1.00 par value, of
Commerce (the "Commerce Common Stock").
 
  CBI will also acquire the assets and assume the liabilities of the Bank in
exchange for shares of Commerce Common Stock (the "Acquisition"). The shares
of Commerce Common Stock acquired by the Bank will then be distributed to the
stockholders of the Bank (other than Commerce, CBI or Shawnee) in a
liquidation of the Bank.
 
  In connection with the transactions contemplated by the Acquisition
Agreement, Commerce will file with the Securities and Exchange Commission (the
"Commission") a Registration Statement on Form S-4 (the "Registration
Statement") relating to the registration under the Securities Act of the
shares of the Commerce Common Stock to be issued in the Merger and
Acquisition.
 
  In connection with this opinion, we have examined and are familiar with
originals or copies, certified or otherwise identified to our satisfaction, of
(i) the Registration Statement, (ii) the Articles of Incorporation and By-laws
of Commerce, as in effect on the date hereof, (iii) the Acquisition Agreement
and (iv) certain resolutions of the Board of Directors of Commerce relating to
the Merger and Acquisition. We have also examined originals or copies,
certified or otherwise identified to our satisfaction, of such documents as we
have deemed necessary or appropriate as a basis for the opinions set forth
herein.
 
  In our examination, we have assumed the legal capacity of all natural
persons, the genuineness of all signatures, the completeness and authenticity
of all documents submitted to us as originals, the conformity to original
documents of all documents submitted to us as certified or photostatic copies
and the completeness and authenticity of the originals of such latter
documents. In making our examination of documents executed by parties other
than Commerce, we have assumed that such parties had the power, corporate or
other, to enter into and perform all obligations thereunder and have also
assumed the due authorization by all requisite action, corporate or other, and
execution and delivery by such parties of such documents on such parties. As
to any facts material to the opinion expressed herein which were not
independently established or verified, we have relied upon oral or written
statements and representations of officers and other representations of
Commerce and others.
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  Members of our firm are admitted to the Bar in the State of Missouri, and we
do not express any opinion as to the laws of any other jurisdiction.
 
  Based upon and subject to the foregoing, we are of the opinion that the
shares of the Commerce Common Stock, when issued upon the consummation of the
Merger and Acquisition in accordance with the terms of the Acquisition
Agreement and as set forth in the Registration Statement, will be validly
issued, fully paid and nonassessable.
 
  We hereby consent to the filing of this opinion with the Commission as an
exhibit to the Registration Statement and to the reference to our firm under
the heading "LEGAL MATTERS" in the related Joint Proxy Statement/Prospectus
which forms a part of the Registration Statement. In giving such consent we do
not thereby admit or imply that we are in the category of persons whose
consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission thereunder.
 
                                          Very truly yours,
 
                                          /s/ Blackwell Sanders Matheny Weary
                                             & Lombardi L.C.
 
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