Poor postcoital tests in infertile patients may be due to dysmucurrhoea, low sperm count, or specific antibodies against spermatozoa. Using a latex agglutination test ("Sperm-antibody-slide-test", Fa. Biotec, Hannover), we examined the cervical and uterine secretions of the patients for sperm antibodies. The results showed a close correlation between a positive sperm-antibody-test and a poor postcoital test, especially in those couples with regular sperm quality. Also in cases with normal postcoital tests, positive sperm-antibody titers can be observed. Therefore, the sperm-antibodies may disturb fertilization in infertile patients even without causing immobilization or agglutination of the spermatozoa in the female genital tract fluids. The determination of the spermatozoa-antibody content in the cervical and uterine secretions must be regarded as an improvement in the diagnostic procedure in human infertility.