The effect of intranasal, synthetic LH-RH (Hoe 471) on undescended testes was investigated in: I. a double blind study comprising 50 patients given either placebo or 0.6 mg LH-RH daily and II. an open study comprising 50 patients with a daily dosage of 1.2 mg LH-RH. In both studies LH-RH was given for 4 weeks. Since some patients had bilateral undescended testes, 116 testes were treated in total. Patients' ages varied between 1 1/2 and 10 1/2 years, with a mean of 5 years. Clinical examination before, during and at end of treatment was performed by both the authors independently. In the placebo group, one testicular descent was seen, indicating difficulty in diagnosis. A therapeutic result, i.e. a significant move from the pretreatment location towards the bottom of the scrotum was seen in 60% of the testes, complete descent being seen in about 40%. In a follow-up study 6 months after treatment, in 23 cases with complete descent from a pretreatment inguinal position, relapse was seen in 5 patients (2 were located at scrotal neck, 3 at the pretreatment position i.e. inguinal). The best results were seen on testes located not too far from the scrotal neck, with the higher dosage of LH-RH and in patients less than 6 years of age. No significant hormonal changes (testosterone-, LH- or FSH-levels in peripheral blood) were seen during the study. Side effects were negligible.