The endocrine function of the human testis in regard to sexuality.

It is well known that the testes play a determining role in male sexuality. However, the exact interrelations between endocrine testicular function and sexual behaviour are not well understood. If these interrelations are to be investigated a number of factors influencing testicular function have to be considered: circadian and seasonal variations, age-related changes, body constitution, physical activity and drug interactions, as well as the influence of endocrine and non-endocrine diseases. The paper emphasizes the complexity of the field and warns against seeing correlations between single random plasma sex hormone determinations and sexual behaviour.