The proliferative activity and level of aberrant mitoses in the cells of the bone marrow were studied experimentally on 223 noninbred mice treated with carminomycin administered intraperitoneally in single (LD50) and repeated doses. When the antibiotic was used in a single dose the values of the mitotic activity of the bone marrow elements did not correspond to the severity of depression and thir quantitative composition, which was explained by an impairement of the mitosis quality and possible interkinetic destruction of a significant part of both erythroid and immature myeloid cells capable of division at early stages after the exposure. At the same time the level of the bone marrow devastation under conditions of the treatment with repeated doses was mainly determined by inhibition of the erythronormoblast proliferative activity.