In order to determine whether bacterial infection of the gonads may account for some male-related infertility, the fertility status of 45 young men who developed gonococcal urethritis and then epididymo-orchitis were studied prospectively. The fertility potential of the subjects was evaluated through history of paternity, repeated semen examinations, serum follicle-stimulating hormone determinations, and testicular biopsy. Before infection, 14 married men (100%) had proved their fertility through their children. Two years after infection, only 21% of these fathers and 40% of all subjects produced semen considered adequate for conception. The semen values in the rest were comparable to those of infertile/subfertile men. Although the lesion was clinically confined to one testis, testicular biopsy and follicle-stimulating hormone studies showed that testicular damage involved both testes. The study showed that bacterial gonadal infection may result in permanent azoospermia or oligospermia and this without question may result in male-related barrenness.