Androgens may contribute to higher cardiovascular risk in men via deleterious effects on vascular endothelial cells (EC). We examined the effects of androgens on male human umbilical vein EC (EA.hy926) in culture. [3H]Thymidine incorporation assays showed that after 24-h serum deprivation, testosterone (T) (but not dehydroepiandrosterone nor 17β-E2) induced significant dose-dependent decreases in DNA synthesis (10-16% at 1-100 nmol/liter); the AR antagonist flutamide (100 nmol/liter) abolished this effect of T. After 48-h serum deprivation, typical apoptotic DNA patterns were detected in agarose gels, and the number of floating cells indicative of severe damage was significantly greater after T treatment for 48 and 72 h (13.7 ± 0.5% and 30.2 ± 2.5%, respectively) than the control values (9.7 ± 1.05% and 23.7 ± 3.0%). Analysis of attached cells by annexin V-fluorescein isothiocyanate/propidium iodide staining showed that after 48-h serum deprivation, T significantly increased the number of cells in the early (16.0 ± 1.1%) and late (8.3 ± 0.3%) stages of apoptosis compared with control (6.8 ± 1.0% and 4.0 ± 0.2%, respectively); such increases in apoptosis-related damage were also observed, to a lesser degree, in serum-enriched culture. Western blotting showed that B cell leukemia/lymphoma-2 protein (Bcl-2) expression decreased significantly in serum-deprived EC treated with T. Thus, T reduces DNA synthesis and enhances apoptosis after serum deprivation in EC, possibly related to reduced Bcl-2 expression.