OBJECTIVE: The null hypothesis of our study is that the success of in vitro and in vivo murine fertilization and embryo development is not decreased by gamete exposure to peritoneal fluid from superovulated patients with endometriosis. STUDY DESIGN: A murine in vitro fertilization model was used to test the effects of endometriosis versus nonendometriosis peritoneal fluid at concentrations of 1%, 5%, and 10% versus an unsupplemented control. Fertilization and blastocyst formation were compared by analysis of variance. In a second experiment superovulated mice were given intraperitoneal injections of endometriosis or nonendometriosis fluid or saline solution 8 hours after human chorionic gonadotropin and then mated. Some mice were killed 3 days after coitus to assess embryo number, cleavage stage, and uterine versus tubal position by means of analysis of variance and covariance with repeated measures. Others were killed 12 days after coitus with the mean number of implantations per animal between groups compared by Student's t test. RESULTS: In vitro fertilization rates decreased as peritoneal fluid concentration increased in both the endometriosis (65%, 43%, 33%) and nonendometriosis (65%, 52%, 35%) groups at 1%, 5%, and 10% peritoneal fluid concentration, respectively. Mice receiving intraperitoneal endometriosis or nonendometriosis fluid or saline solution injections showed no differences in embryo number, cleavage, uterine versus tubal position, or mean implantation number. CONCLUSION: Peritoneal fluid from superovulated patients had no differentially negative effect when compared with the effect of nonendometriosis peritoneal fluid on murine in vitro or in vivo fertilization and embryo development, tubal embryo transport, or implantation.