The immunobead test was used to study the immunoglobulin class of antibodies on sperm before and after penetration through a microcolumn of cervical mucus. Sixteen men with positive sperm antibodies (positive sperm immobilization test) and sperm that penetrated cervical mucus in prior tests were selected for study. However, at the time of study, sperm from seven subjects could not be recovered from the microcolumn. The nine subjects from whom motile sperm were obtained after passage through the column had better sperm mucus penetration tests, lower proportions of sperm binding to anti-IgA immunobeads, and higher proportions of sperm with tail-tip-only binding. Sperm recovered after penetration through the mucus microcolumn displayed a greatly reduced binding to anti-IgA immunobeads in all nine subjects, whereas similar reductions in anti-IgG binding occurred only in four subjects. These results confirm that IgA and sperm-head-directed antibodies are more important than IgG and sperm tail-tip-directed antibodies in impairing sperm penetration of cervical mucus.