ABSTRACT: We studied the proliferation of human peripheral blood lymphocytes from 20 donors stimulated by acrosomal enzymes from ejaculated spermatozoa from healthy individuals. We extracted the acrosomal enzymes without detergent. The amount of proteins in the acrosomal preparation and its proteolytic activity was estimated. The acrosomal preparation was added to auto- and allogeneic lymphocytes in microculture system. Stimulation of lymphocytes was measured by incorporation of 3H-methyl-thymidine after 3 and 6 days of culture. Auto- and allogeneic lymphocytes that were subjected to the action of an acrosomal preparation in in vitro cultures showed stimulation in a 3-day culture at a final concentration of acrosomal proteins of 3.75-7.5 μg per culture. This observation suggests that the mitogenic properties of enzymatic factors are present in acrosomes of spermatozoa.