Mucosal immunity in the female reproductive tract is influenced by immunoglobulins (Igs), cytokines, and reproductive hormones. Previous studies of reproductive-aged women demonstrated that IgA and IgG increases in cervical mucus corresponded to elevated levels of IL-1beta which occurred 1 day before the peak of endogenous estradiol production prior to ovulation. We sought to determine the effect of exogenous hormones on reproductive tract immunity in women on oral contraceptive pills (OCPs) and to compare the results with respect to naturally cycling women. Twelve women of reproductive age who had negative cervical cultures, a normal pap smear, and agreed to abstain from sexual intercourse during the study initiated OCPs. Cervical mucus and vaginal washes were collected at six intervals (2-3 days apart) throughout the treatment cycle. Fifteen naturally cycling women had similar samples collected prior to, during, and subsequent to ovulation. Cervical mucus samples were assayed for IgA, IgG, IL-1beta, IL-6, and IL-10 by enzyme-linked immunosorbent assay (ELISA). IgA, IgG and IL-1beta levels in women on OCPs paralleled increasing levels of norethindrone. Mean values of IgA increased from a low of 14.4+/-3.1 to 41.1+/-9.4 mg/dl and decreased significantly after the cessation of the pills (P < 0.001). In naturally cycling women, the largest quantities of Igs were detected prior to ovulation. By comparison, mean values of IgA in the cervical mucus of women on OCPs (24.4 mg/dl) exceeded peak levels of IgA in the cervical mucus of naturally cycling women (14.6 mg/dl). IgA was the predominant Ig detected in cervical mucus of women on OCPs. Both immunoglobulins in each group exhibited changes relative to their hormonal status. The increased levels of IgA in the cervical mucus of women on OCPs may explain the clinical observation of a lower incidence of sexually transmitted diseases.