The estrogenic activity of environmentally relevant doses of endosulfan was investigated using an animal model. Ovariectomized adult rats were injected once a day for 3 days with sesame oil (control), 0.02mg/kg/day 17beta-estradiol (an uterotrophic dose; UE(2)), 0.0002mg/kg/day 17beta-estradiol (a non-uterotrophic dose; NUE(2)), or 0.006, 0.06, 0.6 or 6mg/kg/day endosulfan. After 24h of treatment, the uteri were weighed (uterotrophic assay) and the luminal epithelial cell height (LECH) and progesterone receptor (PR), and estrogen receptor alpha (ERalpha) protein levels were measured. PR, ERalpha, and complement factor-3 (C3) mRNAs were evaluated using real-time PCR. Uterine weight and LECH were only increased in UE(2)-treated rats. PR, ERalpha and C3 expression levels were modified in most of the endosulfan-treated groups, showing an identical pattern of expression to the NUE(2)-group. Our results show that the pesticide endosulfan mimics non-uterotrophic E(2) actions, strengthening the hypothesis that endosulfan is a widespread xenoestrogen.