THELEN REID & PRIEST LLP
                            40 WEST 57TH STREET
                            NEW YORK, NY  10019


                                                       Exhibit 5(b)

                                                  February 18, 1999



          MDU Resources Group, Inc.
          Schuchart Building
          918 East Divide Avenue
          P.O. Box 5650
          Bismarck, North Dakota 58501


          Ladies and Gentlemen:

                    With reference to the Registration Statement on Form S-
          8 to be filed on or about the date hereof with the Securities and
          Exchange Commission (the "SEC") by MDU Resources Group, Inc. (the
          "Company") under the Securities Act of 1933, as amended (the
          "Act"), and pursuant to which the Company intends to register one
          (1) additional share of its Common Stock, par value $3.33 (the
          "Stock"), and the Preference Share Purchase Right attached
          thereto (together with the Preference Share Purchase Rights
          attached to the shares of the Company's Common Stock, which
          shares of Common Stock are being moved and carried forward to the
          Registration Statement from Registration Statement No. 333-06103
          and Registration Statement No. 333-06105, the "Rights"), for
          offer and sale in connection with the MDU Resources Group, Inc.
          401(k) Retirement Plan, we are of the opinion that: 

                    1.   When

                    (a)  appropriate authorizations by the Federal Energy
                         Regulatory Commission, the Montana Public Service
                         Commission and the Public Service Commission of
                         Wyoming with respect to the issuance and sale of
                         the Stock shall have been granted;

                    (b)  the Company's Board of Directors or a duly
                         authorized committee thereof shall have approved
                         the issuance and sale of the Stock by the Company;
                         and

                    (c)  the Stock shall have been duly issued and
                         delivered for the consideration set forth in the
                         aforesaid Registration Statement and in accordance
                         with the actions hereinabove mentioned,

          the Stock will be validly issued, fully paid and non-assessable.


                    2.   The Rights, when issued as contemplated by the
          Registration Statement, will be validly issued.

                    We are members of the New York Bar and do not hold
          ourselves out as experts on the laws of any other jurisdiction. 
          Our opinions expressed above are limited to the law of the State
          of New York, the General Corporation Law of the State of Delaware
          and the Federal laws of the United States.  As to all matters of
          Montana, North Dakota, South Dakota and Wyoming law, we have
          relied upon the opinion to you of even date herewith of Lester H.
          Loble, II, Esq., Bismarck, North Dakota, the Company's General
          Counsel, which opinion is to be filed as an exhibit to the
          Registration Statement.

                    We hereby consent to the use of this opinion as an
          exhibit to the Registration Statement.  In giving the foregoing
          consent, we do not thereby admit that we belong to the category
          of persons whose consent is required under Section 7 of the Act,
          or the rules and regulations promulgated by the SEC thereunder.

                                        Very truly yours,


                                        /s/ Thelen Reid & Priest LLP
                                                                     
                                         THELEN REID & PRIEST LLP