Poikilocytosis was observed in peripheral blood smears obtained from dogs given doxorubicin. Concurrent administration of thyroxine and ICRF-187 did not prevent the occurrence of poikilocytosis in doxorubicin-treated dogs. Administration of N-acetylcysteine with doxorubicin resuled in mild increase in the extent of poikilocytosis changes were not accompanied by adverse clinical signs referable to the doxorubicin-induced alterations in erythrocytes.