SAA and SIA were assayed in the sera of 172 infertile couples and in the CM of the women and 18 control subjects. Complete infertility evaluation was performed in all subjects except the controls. Results of these studies were correlated with PCT's. Sperm antibodies were detected in the CM of 25.6% of infertile women and in the sera of 12.7% of female and 6.4% of male subjects. No sperm antibodies were found in the CM of controls. Sperm antibodies were present exclusively in sera of 8.1% of women and in the CM of 20.9%. In only 4.7% both serum and CM contained antibodies. A significantly higher incidence of sperm antibodies was found in the sera of women and in CM and sera of all couples with unexplained infertility compared to those with explained infertility. The presence and the number of liver spermatozoa in CM collected for PCT's were found to be significantly related to the existence of SAA and SIA in CM and serum. Stepwise multiple regression analysis indicated that SAA or SIA antibodies in CM and SAA in female serum have a significant negative correlation with endocervical PCT, whereas sperm motility has a positive correlation. These factors, together, accounted for 24.5% of variance. These data indicate that the appearance of SAA and SIA in CM is not related to their presence or titer in blood serum and that the PCT is a reliable screening method when sperm antibodies are suspected to exist in CM and to a lesser extent in serum.