Levels of plasma follicle-stimulating hormone, luteinizing hormone and testosterone in men of proven fertility were compared with those of oligospermic and azoospermic men. The mean level of follicle-stimulating hormone was much higher in the subfertile group, showing a positive association with low sperm count and gonadal histologic defect. The mean level of luteinizing hormone also showed a significant rise with declining sperm density, but no significant statistical difference was observed between the oligospermic and azoospermic patients. Although there was a rise in the mean level of plasma testosterone with poor sperm density, the values were within the normal range. Hormone studies are recommended for investigating male infertility to help delineate men with pregonadal of primary gonadal defects.