The present investigation studied the effects of sperm immunization in the gastrointestinal tract on anti-sperm antibody production and fertility in female mice. For comparative purposes, mice were also immunized with sperm intraperitoneally. Intraperitoneal immunization with 5 X 10(6) washed epididymal and vas deferens sperm 3 times per week for 7 wk produced anti-sperm IgG in plasma at 1:20,000 and in vaginal washings at 1:100 as determined by ELISA. Such mice have been shown previously to have reduced fertility. In comparison, mice immunized intragastrically with 5 X 10(6) sperm once per week for 11-14 wk had anti-sperm IgA in vaginal washings at only about 1:8 as determined by ELISA. After mating at the 14th wk these mice delivered 6.5 +/- 1.4 pups, which was not significantly different from the 7.1 +/- 1.1 pups delivered by an untreated control group. Mice immunized twice intragastrically and once intravaginally during a 25-day period had no detectable anti-sperm IgA in vaginal washings by ELISA. These mice delivered 9.7 +/- 1.2 pups after mating beginning on day 32, as compared to 9.7 +/- 0.8 pups in a PBS-sham immunized group. Mice immunized once intraduodenally and then once intraperitoneally 14 days later delivered 10.4 +/- 0.9 pups after mating 10-14 days after the second immunization, while a similar group of mice whose primary sperm immunization was directly into Peyer's patches delivered 9.0 +/- 1.4 pups. We could not detect anti-sperm IgG or IgA bound to sperm in the uterine or oviduct lumen using immunohistochemical labeling after any of the groups of immunized mice were mated.(ABSTRACT TRUNCATED AT 250 WORDS)