A 13-year-old boy visited our hospital with the chief complaint of right undescended testis and retardation of secondary sexual characteristics. Central hyposmia and sensorineural hearing loss were found. The plasma levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were low and the reaction to LH-releasing hormone (RH) test was poor. After repeated LH-RH tests, a good response in plasma levels of LH and FSH was observed. The diagnosis of Kallmann's syndrome was made from the above findings. The testicular biopsy specimen from him showed immature testis without any developed Leydig or Sertoli cells. To induce secondary sexual characteristics, 2000 I.U. of human chorionic gonadotropin (hCG) was administered to him twice a week for 3 months. The administration of hCG resulted in elevation of plasma testosterone level, swelling of testes, increase of pubic hair and spurt of height.