N-1,N-2-disubstituted polyform-, acet- and -benzamidines containing the 4,4’-substituted diphenyl methane unit were studied by means of H-1, C-13 and N-15 nuclear magnetic resonance (n.m.r.) in solution. The n.m.r. signals were assigned. For the polyacet- and -benzamidine slow tautomerism on the n.m.r. time scale resulted in separate signals for the amino and imino moiety due to preference for the E-anti configuration of the amidine group. This tautomerism was much faster for the polyformamidine due to cyclic dimerization of formamidine groups in the preferred E-syn configuration. In this case, the signals of the amino and imino moiety coalesced.