Thymoquinone is a nutrient with anticarcinogenic activity by stimulating suicidal death of tumor cells. Similar to nucleated cells, erythrocytes may experience suicidal death or eryptosis, characterized by exposure of phosphatidylserine at the erythrocyte surface and by cell shrinkage. Triggers and signaling of eryptosis include increase in cytosolic Ca(2+)activity, ceramide formation, and stimulation of protein kinase C. The present experiments explored, whether thymoquinone influences eryptosis. According to annexin V-binding, thymoquinone (3 microM) increased the percentage of phosphatidylserine-exposing erythrocytes. According to forward scatter in FACS analysis, thymoquinone (10 microM) led to cell shrinkage. The effect of thymoquinone was not paralleled by appreciable ceramide formation (immunofluorescent antibody) or hemolysis (hemoglobin release). It was not significantly blunted in the nominal absence of extracellular Ca(2+) but was inhibited by staurosporine (500 nM). In conclusion, thymoquinone triggers suicidal erythrocyte death, an effect paralleling the apoptotic effect on nucleated cells.