PURPOSE: Recent studies indicate that widely used chemotherapeutic agents induce apoptosis in susceptible cells. One of the effector arms in this cell death pathway is composed of cysteine proteases belonging to the caspase family. In cells, caspase-3 has been shown to play an important role as a downstream member of protease cascade, where various cell death pathways converge into the same effector pathway. JNK, a member of the mitogen-activated protein kinase pathway, is activated in response to many stressful stimuli including heat shock, UV irradiation, protein synthesis inhibitors, and inflammatory cytokines. In this study, we investigated whether JNK1 & caspase-3 play a role in the apoptosis induced by adriamycin (ADR). METHODS: U937 cells were cultured in RPMI 1640 and treated with different concentrations of ADR. Cellular DNA was extracted and analyzed by electrophoresis on a 1.5% agarose gel to detect DNA fragmentation. The activity of caspase-3 was measured by the proteolytic cleavage of the fluorogenic substrate DEVD-AMC. The activity of JNK1 was measured by in vitro immunocomplex kinase assay with 2 microgram of GST-c Jun as a substrate and quanititated using phosphoimager analyzer. RESULTS: ADR induced the apoptotic death of U937 myeloid cells in a dose-dependent manner, which was characterized by increasing ladder-pattern DNA fragmentation. Consistent with apoptotic death of U937 cells, ADR induced the catalytic activation of caspase-3 as well as JNK1 at 2.5 microgram/mL of concentrations. CONCLUSION: Adriamycin induces apoptosis of human myeloid leukemic U937 cells via activation of caspase-3 and cJun-N terminal kinase1 (JNK1)/Stress activated protein kinase (SAPK).