Cytokines released by various cell subsets in the male urogenital tract are capable of markedly influencing sperm function and fertility. Interleukin-6 (IL-6) levels were determined by "sandwich" enzyme immunoassay in the seminal plasma of 77 men divided as follow: (1) into 7 groups according to the etiological diagnosis of fertility, and (2) into 2 groups on the basis of normal or abnormal spermiogram. There was a statistically significant association between IL-6 and the patients' status (P < 0.0014). These results are due to statistically significant differences between the groups with infection of the accessory genital glands and normal controls, as well as between the groups with infection of the accessory genital glands and that with varicocele, indicated by the Honestly Significant Differences (HSD) test for multiple comparisons. There was no significant difference of IL-6 levels between men with normal and those with abnormal spermiograms. Furthermore, there was no correlation between IL-6 levels and the variables of the spermiogram. The prostate seems to be the main site of origin of IL-6 in the seminal plasma. Our data suggest that urogenital infections may lead to elevated levels of IL-6 in the seminal plasma. This measurement of IL-6 in semen may provide clinically useful information for the diagnosis of male accessory gland infection.