Objective: In women, sex hormones cause increased morbidity and mortality in patients with coronary heart disease (CHD) and adversely affect the coagulation profile. We have studied the effect of physiological testosterone replacement therapy in men on coagulation factor expression, to determine if there is an increased risk of thrombosis. Methods: Double-blind, randomized, placebo-controlled trial of testosterone in 46 men with chronic stable angina. Measurements of free, total and bioavailable testosterone, luteinising hormone (LH) and follicle-stimulating hormone (FSH), estradiol, plasminogen activator inhibitor-1 (PAI-1), fibrinogen, tissue plasminogen activator (tPA) and full blood count were made at 0, 6 and 14 weeks.