Antibodies delivered directly to the vagina can provide passive immunoprotection against pregnancy and sexually transmitted disease. The duration of protection is limited by the residence time of the antibodies in the vagina; to our knowledge such residence times have not been reported. We investigated the time-course of disappearance of IgG delivered to the mouse vagina using three different methods to monitor the amount of administered IgG remaining in the vagina: gamma counting of 125I-IgG, viral neutralization of unlabeled monoclonal anti-herpes virus IgG2a, and ELISA of biotinylated IgG. The test IgG was delivered to the vagina in saline and recovered by lavage. All three methods yielded similar results, suggesting that the residence half-life is not significantly affected by the volume administered, phase of the estrous cycle, or labeling of IgG. In awake mice, a significant fraction of IgG disappeared with a relatively short half-life, (t1/2)alpha, of 0.7 +/- 0.1 h; but this rapid (alpha phase) decrease did not occur in anesthetized mice, suggesting that the movements of awake mice expel some of the test IgG-saline solution from the vagina. Over the next 25 h, the test IgG disappeared with a residence half-life, (t1/2)beta, of 5 +/- 2 h. We believe this slow elimination of IgG may depend on the rate that mucus secretions are shed from the vagina.