NHLBI convened a Trans-NIH Estrogen Working Group to make recommendations to NHLBI on the feasibility of undertaking a clinical trial of the effects of postmenopausal estrogen use on cardiovascular disease mortality. The Working Group identified a number of important research questions which needed to be answered to elucidate the effects of postmenopausal estrogen use on risk factors for cardiovascular disease and osteoporosis. This initiative was the result of the Working Group's deliberations and recommendations.