Androgens have two principal actions in the male, i.e. to maintain spermatogenesis in the testis and to exert anabolic- androgenic effects in peripheral tissues. The levels of androgens in different compartments of the body vary greatly, and also throughout life their levels undergo dramatic changes. Therefore, it is relevant to ask what the necessary levels of testosterone are to maintain its diverse functions. The concentration of intratesticular testosterone is about 100-fold higher than in the periphery. It has been proposed that such a high intratesticular testosterone level is needed to maintain spermatogenesis, but a simpler explanation is that the level is high only because the testis is the site of synthesis of this hormone for the needs of the whole body. Another controversy surrounds the importance of the declining androgen levels in ageing men. Do they mean that hypogonadism upon ageing is a common phenomenon, in analogy with female menopause, or do the lower androgen levels in ageing men maintain their peripheral anabolic-androgenic status? The purpose of this lecture is to discuss the varying needs of androgens in the testis and periphery at different times of the man's life span, based on recent experimental and clinical data.