Carboplatin injected intravenously in a maximum permissible dose to Wistar rats inhibited erythro- and granulocytopoiesis in the bone marrow, caused hyporegenerative anemia, leukopenia, and thrombocytopenia in the peripheral blood, led to hypoplasia of the thymus and spleen, and produced moderate apoptosis-inducing effects. These effects were observed within the first month after treatment. In mice carboplatin induced chromatid aberrations in the bone marrow and increased the count of erythrocytes with micronuclei. Moderate hypoplasia of erythro- and granulocytopoiesis and accelerated involution of the thymus were observed 3 and 6 months after cytostatic treatment. Our results indicate that carboplatin possesses higher myelotoxic activity compared to cisplatin.