A quantitative analysis of spermatogenesis in mice and rats has shown that the response of various germ cells to cytotoxic effects of Dipin or NMU differs. The spermatogonial compartment consisting of actively proliferating cells and some stem cells are the main targets for these drugs. The advanced I order spermatocytes, spermatids and spermatozoa proved to be less susceptible. Species specific differences have been established in the character of destructive and restorative processes during spermatogenesis.