The presence of circulating agglutinating anti-sperm antibodies as cause for unexplained infertility of artificially inseminated buffalo cows was assessed. An attempt to identify buffalo sperm isoantigens was also made. The following methods were applied for that purpose: the tray agglutination test (TAT), SDS-polyacrylamide gel electrophoresis, and immunoblotting. The results obtained showed that three of 90 sera from buffalo cows with unexplained infertility were positive in TAT (3.3%) and their titers were low. A total of 27 spermatozoal polypeptides reacted positively with the IgG-isoantibodies of one of the sperm agglutinating sera in immunoblotting. Of the control sera 12 also revealed individual variations in the number of positive fractions on the blots. On the basis of comparing the blot with the positive sperm agglutinating serum to the blots of the positive controls, two buffalo sperm isoantigens were identified, with the respective molecular weights of 40 kDa and 120 kDa. In conclusion, circulating agglutinating anti-sperm antibodies are very rarely detected in buffalo cows with unexplained infertility after several artificial inseminations.