We measured the gonadotropin response pattern to the intravenous injection of luteinizing hormone-releasing hormone in 53 male adolescents 11 to 17 years old (average age 14.2 years) with a grade II to III varicocele. Volume loss of the testis ipsilateral to the varicocele of 2 cc or more was noted in 32 patients. Baseline serum levels of follicle-stimulating hormone, luteinizing hormone and testosterone were determined, and measured again at 15, 30 and 60 minutes following intravenous injection of luteinizing hormone-releasing hormone. Of the patients 23 had an exaggerated response pattern following luteinizing hormone-releasing hormone stimulation, including abnormally high post-stimulation levels of luteinizing hormone only in 6, follicle-stimulating hormone only in 4, and follicle-stimulating and luteinizing hormones in 13. No significant difference in mean age, testosterone levels or loss of testicular volume was noted between the abnormal and normal response groups. This study indicates that approximately 45 per cent of adolescents with a varicocele have evidence of testicular injury. The physical examination was of no value in predicting which patient with a varicocele would display evidence of testicular dysfunction. We suggest that the luteinizing hormone-releasing hormone stimulation test become a routine part of the evaluation of an adolescent with a varicocele.