Immunity at mucosal surfaces, which are ports of entry for many pathogens, is essential in preventing infections. But most current strategies for passive immunization involve injection of antibodies for systemic, not mucosal, protection. We measured mucosal and systemic antibody levels after controlled topical delivery to the vagina. Poly(ethylene-co-vinyl acetate) disks containing 125I-labeled monoclonal IgG or anti-lactate dehydrogenase-C4 antibodies were placed in the vaginas of mice. High antibody levels (0.26-12 micrograms/ml) were maintained at the mucosal surface for 7 days after disk insertion. Antibody molecules also penetrated into the vaginal epithelium, presumably by diffusing through the extracellular space, and entered the circulation. Biologically active antibodies were detected in the blood. The antibody concentration in the blood was approximately 1% of the concentration in the vagina. Although the permeability of the epithelium to macro-molecules is low, high concentrations were maintained at the luminal surface for an extended period, permitting substantial systemic uptake of antibody.