Prepubertal male cancer patients facing gonadotoxic therapy cannot be offered a procedure to create a fertility reserve, in contrast to the options available for men. Sperm production by testis xenografting has been proposed for boys, but as the efficacy of sperm production in animal trials is low, hormonal stimulation of recipients carrying xenografts has been proposed to enhance graft development. We confirm that spermatogonia are the only germ cells present in immature rhesus testis. We xenografted immature tissues into nude mice and treated them with human chorionic gonadotropin (hCG) at a low (1IU) and high (10IU) dose twice weekly for 3months. We observe significantly larger grafts in treated recipients, and significantly larger recipient body weight and seminal vesicle weight in the high dose group. However, histological analysis demonstrates that no significant increase in seminiferous maturation is induced by hCG treatment. Moreover, grafts in control recipients develop spermatozoa within 5months. Thus, although hCG treatment of hosts enhances the growth of xenografted prepubertal primate testis tissue and stimulates androgen production in the grafts, the treatment does not enhance the differentiation of the seminiferous epithelium. © 2011 The Authors. International Journal of Andrology © 2011 European Academy of Andrology.