500 infertile patients (250 with and 250 without left side varicocele) and 33 fertile men were evaluated as far as seminal parameters and the hormonal status were concerned. Sperm motility was constantly lower in infertile patients also when infertile group was compared to fertile one with the same sperm density. Serum testosterone levels were lower in infertile groups when compared to fertile men, and this confirms the existence of an androgenic deficit as a common finding in infertility associated or not to varicocele. FSH and LH increased (p less than 0.001) when sperm density dropped to less than 5 X 10(6) spermatozoa/ml. A negative correlation was found between both gonadotropins and sperm count (p less than 0.001), also after exclusion of azoo- and oligozoospermic (less than 5 X 10(6) spermatozoa/ml) patients (p less than 0.01). Gonadotropins were moreover tightly correlated between each other (p less than 0.001). Our data suggest that both gonadotropins are tightly tuned with sperm output and thus with the spermatogenic potential.