The male reproduction system is dependent on hormones. These chemicals that stimulate or regulate the activity of cells or organs. The primary hormones involved are are follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone. FSH and LH are produced by the pituitary gland, and is located at the base of the brain and responsible for many functions in the body. FSH is necessary for sperm production (spermatogenesis). LH stimulates the production of testosterone, which is necessary to continue the process of spermatogenesis. Testosterone is also important in the development of male characteristics, including muscle mass, strength, fat distribution, bone mass and sex drive.