Thirty-four married couples with clinically unexplained infertility and normal spermiograms in all male partners were investigated for sperm antibodies by means of the sperm agglutination, sperm immobilization and sperm immunofluorescence test. In 50% of the couples, sperm antibodies were found in at least one of the partners and with at least one of the tests, e.g. ten times in the female partner alone, six times in the male partner alone, and once in both partners. The correspondance of the three tests was astonishingly low; it is assumed, therefore, that they indicate different types of antibodies. On the basis of the present investigations it is not possible to assess which type of antibody is responsible for the infertility of the female or male partner respectively. This seems only possible when the decrease of certain antibody types can be determined after a period of no antigen contact (avoidance of sperm contact) and when conception has taken place. The significance of autoanti bodies against sperm in clinically healthy men with normal spermiograms remains open.