Androgens play a number of important physiological roles in the human. In the male, testosterone is required for virilization, normal sexual function, and both stimulation and maintenance of bone and muscle mass. Epidemiological studies have shown a progressive decline in testosterone levels with ageing in men. The clinical significance of this decline is still unclear, and there is controversy as to whether a specific syndrome of androgen deficiency or 'andropause' exists. The benefits of testosterone supplementation in this age group have yet to be equivocally established, and long-term safety data on testosterone administration in this setting are lacking. In the female, a decline in testosterone levels with ageing has been less clearly established due, at least in part, to the absence of sensitive assays. Available data suggest that the major role of testosterone replacement after menopause may be in those women who have had an oophorectomy.