LHRH tests (100 μg iv) were performed in 11 normal male volunteers before and after administration of 100 mg clomiphene citrate per os for 7 days. Serum FSH, both pre and post LHRH levels (peak value and area under response curve) were significantly increased (P < 0.01) by clomiphene citrate, while the maximum increments of FSH above baseline (ΔFSH) and area under response curve from basal level (Δarea) were unchanged. On the other hand, basal serum LH levels increased significantly (P < 0.005), post LHRH levels did not change by clomiphene citrate, whereas the increments after LHRH administration (both ΔLH and Δarea) decreased significantly (P < 0.05) on the second LHRH test. Basal levels of testosterone increased following clomiphene citrate treatment (P < 0.005). The increased testosterone is considered to suppress the effect of LHRH on LH secretion.