Mont. Code Ann. § 35-4-205

Professional corporations may be organized under this chapter only for the purpose of rendering professional services and services ancillary thereto within a single profession, except that a professional corporation may be incorporated for the purpose of rendering professional services within two or more professions and for any purpose or purposes for which corporations may be organized under the Montana Business Corporation Act to the extent that such combination of professional purposes or professional and business purposes is permitted by the licensing laws and rules of this state applicable to such professions.