We studied 48 prepubertal boys with cryptorchidism between 1 year 3 months and 11 years old who were treated with buserelin every other day for 6 months. Urinary luteinizing and follicle-stimulating hormones, and testosterone remained unchanged during the entire treatment period. In boys older than 7 years a slight but significant increase in testosterone was noted in the first morning voided urine at the end of treatment. Testicular biopsies were obtained at orchiopexy in all patients in whom testicular descent was not complete (83 per cent). A significant increase in the number of germ cells was observed in patients with unilateral and those with bilateral cryptorchidism, indicating that 6 months of buserelin therapy improved the fertility status even when testes were in an undescended position during treatment.