An elevated concentration of lipoprotein(a) [Lp(a)] is a potent risk factor for coronary atherosclerosis. Recently, several hormonal agents including estrogen have been reported to decrease serum Lp(a) concentrations. We found that the antiestrogen tamoxifen also decreased Lp(a) concentrations approximately 40% in six patients with breast cancer, an effect that was achieved by 1 month of therapy and that was stable in five of six patients. If the Lp(a)-lowering effect of tamoxifen can be replicated in women without breast cancer, tamoxifen might be considered as an alternative to niacin for the treatment of elevated Lp(a) levels.