As shown in immunochemical experiments alpha- and beta-forms of NAD-kinase from rabbit liver tissue consisted of oligomers involving subunits with molecular mass of 33,000 and 62,000, respectively. Both oligomers of the alpha-type with Mr 180,000 and 150,000 and of the beta-type with Mr 280,000 precipitated with the antibodies produced against the alpha-enzyme of Mr 180,000. Use of immunosorbents produced after immobilization of the alpha- and beta-forms of NAD-kinase on odiphile enabled to estimate the ratio of antigenic determinants in oligomers of both NAD-kinase forms. Subunit of the enzyme beta-form carried 3-fold more determinants than the subunits of the alpha-form. The isozyme nature of the alpha- and beta-forms of NAD-kinase is discussed.