The effects of different dosages of thalidomide, gossypol and dexamethasone on the levels of apoptosis and nitric oxide (NO) production were studied in a human chronic myelogenous leukemic cell line, K-562. Increases in the levels of apoptosis were induced by both 15 and 30 μM of thalidomide but only 15 μM significantly increased NO production. All dosages of gossypol used increased the production of NO and all dosages except 200 μM raised the level of apoptosis. After dexamethasone treatment the level of NO either decreased or stayed constant. Thus, some dosages of thalidomide and gossypol concomitantly raise the levels of apoptosis and NO production, but dexamethasone, though it induced apoptosis, had no significant effect on NO production. © 2004 Elsevier Ltd. All rights reserved.