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Testosterone is the primary hormone responsible for stimulating spermatogenesis in the testes. Produced in the Leydig cells located within the testes, testosterone plays a crucial role in the development and maturation of sperm cells. The process of spermatogenesis involves multiple stages, including the transformation of spermatogonia into mature spermatozoa, and testosterone is essential for initiating and sustaining these developmental processes.

In addition to its direct action on Sertoli cells, which support and nourish developing sperm, testosterone also influences the expression of genes that are critical for sperm production. This regulation promotes the proliferation of spermatogonia and their subsequent differentiation into mature sperm.

Other hormones, such as follicle-stimulating hormone (FSH), work alongside testosterone to regulate spermatogenesis. However, testosterone is the key hormone that drives this process in the testes.