Transplantation of brain tissue from normal donors into the central nervous system of animals with specific central neurochemical deficiencies has been used to remedy such defects. The present studies demonstrate that the hypogonadism present in the adult male hypogonadal (hpg) mouse that is secondary to hypothalamic gonadotropin releasing hormone (GnRH) deficiency can be corrected by grafts into the anterior third ventricle of fetal preoptic area (p.o.a.) tissue. The p.o.a. is a primary site of localization of GnRH neurones in rodents. As compared with untreated hpg males, or with hpg males that had received control cortical tissue implants, the hpg animals with p.o.a. grafts showed measurable levels of GnRH within the hypothalamus. Immunocytochemical studies revealed GnRH within the transplants. Increased pituitary and plasma LH and FSH, and testicular growth with full spermatogenesis, were also evident in the hpg males that had received p.o.a. implants.