[en] The present study showed that the functions of the hypothalamic-pituitary-gonadal and hypothalamic-adrenocortical systems changed in adult male rats thymectomized within 48 h after their birth. Two days later, head irradiation with 10 Gy x-rays was performed in the thymectomized male rats, serum LH and FSH, serum and urine testosterone and corticosterone, pituitary and testicular cAMP and hypothalamic β-EP and L-Enk contents were all reduced in different degrees, except the hypothalamic M-Enk content was increased, indicating that the changes were not in the same direction as those in intact male rats after head irradiation. These results suggest that the changes in head irradiated thymectomized male rats may differ from the changes seen in head irradiated intact male rats because of the influence of thymectomy on the neuroendocrine functions