A double-blind, placebo-controlled study of the efficacy of LH-RH nasal spray in treatment of cryptorchidism involving 252 prepuberal boys with 301 undescended testes, showed a success rate of 9% (14 testes) for LH-RH and 8% (10 testes) for placebo. Including a subsequent open study and a second course of LH-RH as required, the rate for LH-RH rose to 18% (48 testes). The follow-up period saw late descent in another 5% (14 testes), in a few cases coinciding with the onset of puberty. Retrospective evaluation revealed a previous scrotal position of the testes for 43% of the boys with success of treatment and even for 17% of the boys with failure of treatment. In many of these cases surgery revealed an anatomical anomaly that might have caused testicular ascent. Hormonal evaluation revealed no abnormalities in cryptorchid boys compared with control subjects, nor was there a divergence in values before and after treatment. The lower the pretreatment testicular position, the better the rate of success.