We have reviewed 61 reported cases of acute leukemia developing in patients who had previously received immunosuppressive agents for non-neoplastic disorders. In three patients the diagnosis of acute leukemia was made less than six months after the first exposure to immunosuppressive drugs and was, therefore, considered coincidental. Among the remaining 58 patients, most diagnoses were of myeloblastic or myelomonocytic leukemia. The underlying diagnoses in most of the 58 patients were rheumatoid arthritis or renal disease or renal transplant. Thirty patients had received alkylating agents exclusively, 10 had received antimetabolites only, while the remaining 18 patients had received multiple therapeutic modalities including antimetabolites, alkylating agents, and/or radiation. Most patients had also received large amounts of corticosteroids. Although we do not have the overall denominator of population at risk, the relatively high proportion of patients who had received alkylating agents before developing acute leukemia doses suggest a causal relationship, and one might, therefore, hesitate before using such drugs in non-life-threatening diseases.