We have studied IL-2, SIL-2R, and sCD4 concentrations in the seminal plasma of 20 healthy men (controls), 20 oligozoospermics and 20 azoospermics by the "sandwich" enzyme immunoassay technique. We have also measured IL-2, SIL-2R and sCD4 in the two fractions of the split ejaculate of 10 healthy men. Our results show that the mean IL-2 and sCD4 concentrations in the seminal plasma were significantly higher compared to the levels in the serum of normal men; furthermore, there were no significant differences of SIL-2R and sCD4 between the group of normal men and the groups of men with oligozoospermia or azoospermia. On the contrary, significantly higher levels of IL-2 and sCD4 were found in the first compared to the second fraction of the split ejaculates. Our results support the view that the estimation of IL-2 in seminal plasma has value concerning the quality of semen. On the contrary, the estimation of SIL-2R and sCD4 in seminal plasma are valueless concerning normal or abnormal semen. Finally, the prostate seems to be the main site or origin of IL-2 and sCD4.