Loss of the inhibition of apoptosis is important in leukemogenesis and may influence the prognosis. Survivin is an inhibitor of apoptosis that shows selective expression during fetal development and in human malignancies. Survivin expression was examined in human leukemias using the reverse transcriptase-polymerase chain reaction. Survivin gene expression was detected in 17 of 31 patients with acute myelocytic leukemia and 11 of 16 patients with acute lymphocytic leukemia but was not identified in normal bone marrow cells. Survivin expression was lower in patients with M3 acute myelocytic leukemia than in patients with other types of acute leukemia. Survivin was not detected in the chronic phase of chronic myelocytic leukemia but was observed in 5 of 7 patients with chronic myelocytic leukemia in blastic crisis. These findings suggest a relationship between survivin gene expression and hematopoietic cell differentiation. In fact, survivin gene expression was down-regulated during the differentiation of HL-60 cells after treatment with dimethyl sulfoxide or all-trans-retinoic acid. Moreover, the disease-free survival rates of patients with survivin expression were lower than in patients without survivin expression. Accordingly, survivin may have a role in leukemogenesis as well as in other malignancies. Detecting survivin may also provide prognostic information.