Acute nonlymphoblastic leukemias following other blood disorders or exposure to possible oncogenic agents were analyzed for cytological and cytogenetical characteristics. "Secondary' acute leukemias (AL) were often found to be unclassifiable in the FAB system. Monosomy 7 was associated with megakaryocytic cell line abnormalities. Variation of cytological and cytogenetical patterns was correlated in the whole sample and in a sample of 10 postpolycythemia vera blood disorders.