With the aid of histoautoradiography, the proliferation of enterocytes in rat intestinal adenocarcinomas induced with subcutaneous treatment by 1,2-dimethylhydrozine has been studied. The experimental adenocarcinomas are characterized by a high proliferative activity being, however, lower than that in the proliferative zone of the normal intestinal crypt. The parameters of adenocarcinoma proliferation are very close to those of a cell population from the bottom part of crypts in the control animals. This population involves several subpupulations and it is here that stem enterocytes occur. The tumour enterocytes are characterized by the enlargement of short mitotic cycle from 11 to 16 hours, due, mainly, to the prolongation of G1 phase as well as to a more pronounced degree of heterogeneity in relation to the mean tS and tG2 and, probably, to the appearnace of subpopulation R2.