EXHIBIT 5.1
 
                         [LETTERHEAD OF BRYAN CAVE LLP]

                                 August 8, 1996
 
Board of Directors
Bank United Corp.
50 Charles Lindbergh Blvd.
Suite 500
Uniondale, New York 11553
 
Ladies and Gentlemen:
 
     We are acting as special counsel for Bank United Corp., a Delaware
corporation (the "Company"), in connection with various legal matters relating
to the filing with the Securities and Exchange Commission of a Registration
Statement on Form S-4 (the "Registration Statement") under the Securities Act
of 1933, as amended (the "Securities Act"), covering an offer to exchange (the
"Exchange Offer") the Company's 8.05% Senior Notes due May 15, 1998 (the
"Exchange Notes") for a like principal amount of its issued and outstanding
8.05% Senior Notes due May 15, 1998, previously issued and sold to certain
qualified institutional buyers in reliance on, and subject to the restrictions
imposed pursuant to Rule 144A under the Securities Act, as well as to a limited
number of institutional investors that are "accredited investors" within the
meaning of Rule 501 under the Securities Act (such outstanding securities being
collectively referred to herein as the "Rule 144A Notes"). The principal
amount of Rule 144A Notes outstanding on the date hereof is $115,000,000. The
Exchange Notes are to be issued pursuant to an Indenture, dated as of May 15,
1993, and a First Supplemental Indenture, dated as of January 23, 1995
(collectively, the "Indenture"), between the Company and The Bank of New York,
as Trustee, which are filed as exhibits to the Registration Statement.
 
     In connection herewith, we have examined and relied without independent
investigation as to matters of fact upon such certificates of public officials,
such statements and certificates of officers of the Company and originals or
copies certified to our satisfaction of the Registration Statement, the
Indenture, the Exchange and Registration Rights dated as of May 10, 1993,
between the Company and the Purchasers of the Rule 144A Notes, the Restated
Certificate of Incorporation and By-Laws of the Company, proceedings of the
Board of Directors of the Company and such other corporate records, documents,
certificates and instruments as we have deemed necessary or appropriate in order
to enable us to render the opinions expressed below. In rendering this opinion,
we have assumed the genuineness of all
 
                                 BRIAN CAVE LLP
 
Bank United Corp.
August 8, 1996
Page 2
 
signatures on all documents examined by us, the authenticity of all documents
submitted to us as certified or photostatted copies.
 
     We express no opinion as to the applicability or effect of (i) any
bankruptcy, insolvency, reorganization, moratorium or other similar laws
relating to or affecting creditors' rights generally, or (ii) general principles
of equity, including, without limitation, concepts of reasonableness,
materiality, good faith and fair dealing and the possible unavailability of
specific performance, injunctive relief or other equitable remedies, regardless
of whether enforceability is considered in a proceeding in equity or at law.
 
     Based upon the foregoing and in reliance thereon and subject to the
qualifications and limitations stated herein, we are of the opinion that:
 
     (1)  The Company is a corporation validly existing in good standing under
          the laws of the State of Delaware.
 
     (2)  When
 
          i)   the Registration Statement, including any amendments thereto,
               shall have become effective under the Securities Act;
 
          ii)  the Indenture has been duly qualified under the Trust Indenture
               Act of 1939, as amended; and
 
          iii) the Exchange Notes shall have been duly executed and
               authenticated in accordance with the provisions of the Indenture
               and duly delivered to the holders thereof in exchange for the
               Rule 144A Notes;
 
          then the Exchange Notes will be valid and binding obligations of the
          Company.
 
     (3)  The material federal income tax consequences of the Exchange Offer are
          accurately set forth under the heading "Federal Income Tax
          Considerations" in the Preliminary Prospectus dated August  , 1996,
          included in the Registration Statement.
 
     In rendering the opinion expressed in clause (3) above, we have relied upon
the facts as set forth in the Registration Statement. Any variation or
difference in the facts from those set forth in the Registration Statement could
affect our opinion. Such opinion is also based on various statutory provisions,
regulations promulgated thereunder, and
 
                                 BRYAN CAVE LLP
 
Bank United Corp.
August 8, 1996
Page 3
 
interpretations thereof by the Internal Revenue Service and the courts having
jurisdiction over such matters, all of which are subject to change either
prospectively or retroactively.
 
     This opinion is not rendered with respect to any laws other than the
General Corporation Law of the State of Delaware and the federal laws of the
United States.
 
     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to our firm under the caption
"Legal Matters" in the Prospectus included as a part thereof. We also consent
to your filing copies of this opinion as an exhibit to the Registration
Statement with agencies of such states as you deem necessary in the course of
complying with the laws of such states regarding the Exchange Offer. In giving
this consent, we do not admit 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 Securities and Exchange Commission thereunder.
 
                                          Very truly yours,

                                      /s/ BRYAN CAVE LLP
                                          BRYAN CAVE LLP