In males, the testes are responsible for the secretion of the male sex hormone, testosterone.
Testes also produce sperm.
This is the most important sex hormone synthesized in men responsible for attaining puberty in males, muscle mass growth, strengthening the bones and muscles, increasing the bone density, and also controlling facial hair growth.
Testosterone helps in the maturation of male reproductive organs, as well as the development of secondary sex characteristics.
Testosterone is secreted by the testes in response to the luteinizing hormone secreted by the hypothalamus.