Polar organic compounds, such as dimethylsulfoxide and butyric acid, are known to induce differentiation in Friend erythroleukemia cells as well as in other cell types. It has been found that many of the compounds that induce cellular differentiation, inhibit 3H-thymidine incorporation and induce cell damage when incubated with leukemic cells from patients with acute or chronic myelogenous or acute lymphocytic leukemia. These effects are time and dose dependent. Among the compounds tested, butyrate was the most potent. Parenteral administration of butyrate (500 mg/kg/day) for ten days to a child with acute myelogenous leukemia in relapse, and resistant to conventional therapy, resulted in elimination of myeloblasts from the peripheral blood, an increase in mature myeloid cells and a reduction in 3H-thymidine uptake by the patient's peripheral blood cells. Bone marrow myeloblasts were reduced from 70-80% to 20% following the course of intravenous butyrate. No impairment of liver or renal function and no coagulation abnormalities were observed during butyrate treatment. Organic agents that induce cell differentiation may provide additional reagents for the clinical management of selected cases of leukemia.