This study examined the toxic effects of cadmium on the function of sexual hormone release in the ovaries of rats and the mechanism of this dysregulation. In vivo, adult female rats were randomly assigned to four groups based on weight. Cadmium was given ip 5 days/week for 6 weeks at doses of 1.0, 0.5, 0.25 and 0mg/kg. Following euthanasia, the ovaries were removed and placed into culture medium for 3h. The levels of progesterone (P) and estadiol (E) in the culture medium were then measured by radioimmunoassay. In vitro studies were done using the ovaries of adult rats in different stages of estrous (proestrus, estrus, metestrus and diestrus). Individual ovaries were collected, placed into culture medium and exposed to 0, 0.1, 1, or 2mM of CdCl(2) for 3h, at which time the levels of P and E in the ovary culture serum were determined by radioimmunoassay. The in vivo results showed that the levels of P and E in the ovary culture serum (5.3+/-1.4 ng/ml and 1.4+/-0.4 pg/ml, respectively) decreased significantly in the high dose group compared to the control (9.2+/-0.9 ng/ml and 3.9+/-0.7 pg/ml, respectively). In vitro, there were significant differences in P and E in between the different concentrations of cadmium and also between the different stages of the estrous cycle. These data suggest that cadmium can inhibit P and E release in ovaries. This may represent an important mechanism of endocrine disruption.