A register of 746 cases of secondary acute leukemias has been established by reviewing the literature from 1930-1980. Out of these 680 belong to acute nonlymphocytic leukemias, FAB M1-M6. Data have been subjected to a multiparameter analysis in term of previous therapy and subtype characteristics of acute nonlymphocytic leukemia (ANLL). There are indications that secondary ANLL are characterized by the preponderance of early acute myeloblastic leukemias if compared to de novo ones. Furthermore it has been shown that alkylating agents induced decidedly more acute myelomonocytic leukemias whereas irradiation tended to induce more acute myeloblastic leukemia. Since secondary acute leukemias represent a serious late consequence of alkylating agent and irradiation therapy it is high time to find new therapeutical modalities for lymphomas and to consider the withdrawal of alkylating agents from the therapy of autoimmune disorders.