Abstract. Sixty-seven prepubertal boys with either uni-or bilateral cryptorchidism were treated with LH-RH or its analogue Hoe 766. In all cases the undescended testes were located in the inguinal canal; none had retractile testes.A) 23 boys were given 200 lag LH-RH-6 times daily for 7 days B) 24 boys were given 5001ag LH-RH-2 times daily for 7 days C) 10 boys received 100lag Hoe 766 every other day at 8 p.m.for a totaI of 8 insuffiations D) 10 boys received 25lag Hoe 766 every other day at 8 p.m.for a total of 8 insuffiations.The treatment was performed with control by LH-RH tests and testing the pituitary reserve of gonadotropins. Plasma testosterone was measured by RIA. Of the 47 boys treated with synthetic LH-RH, 14 (29.8%) gave a positive response with descent of the testes into the scrotum (A: 21.7%; B: 37.5%). The basal values and the pituitary reserves of LH and FSH did not change after therapy. Plasma testosterone showed an increase in the whole group of patients. Hoe 766 caused an increase in the FSH in all boys, but the curve was significantly higher in group C. There was no difference in plasma testosterone level between group C and D.None of the ten patients in group C responded to the therapy. In three patients of group D (30%) both testes descended. The administration of hCG to those boys who had not responded to the synthetic LH-RH or its analogue therapy led to the descent of three testes in group A and B, of two testes in group C, and of three testes in group D.Treatment of cryptorchidism by synthetic LH-RH or its analogue Hoe 766 for a short time can produce good results. The dosage of the drugs plays an important role in determining its effect.No change was found in gonadotropin secretion induced by synthetic LH-RH nasal spray therapy. The effect of intranasal administration of Hoe 766 is dose-dependent for FSH, but not for LH. When using synthetic LH-RH the best results were obtained by other authors with treatment of at least four weeks. The best results with synthetic or analogue LH-RH treatment were obtained in those subjects whose testes were located closer to the external ring. No side effects were observed either during or after the treatment.

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