The basal hormone and gonadotropin response to an infusion of GnRH were assessed in 22 men with varicocele who had seminal stress pattern and testcular biopsies were performed in 16. The results were as follows: 1. All od plasma testosterone and basal LH values were normal and basal plasma FSH values were elevated in 9 of 22 patients(45.5%). The fact that basal plasma FSH levels elevated often than LH levels suggests that the Sertoli cells are demaged more frequently than are the Leyding cells. 2. Exaggerated response of FSH following GnRH stimulation was found in 2 cases(16.7%) out of 12 patients with normal plasma FSH level. This suggested that the FSH response to GnRH stimulation might be a better discriminant for determining Sertoli cell dysfunction than basal FSH levels. 3. There was no statically difference between varicose size(Grade II vs Grade III) and testicular volume, basal hormonal value or semen parameter. 4. There was statically difference between sperm count and basal plasma FSH levels(p<0.05). In oligospermia patients(<20x10(6)/ml), the palsma FSH level was increased more than that of normal sperm count. These results suggest that the GnRH stimulation test may help to identify varicocele patients with a testicular injury at an early stage of involvement.