Diclofenac is embryotoxic in animals but the mechanism of its embryotoxicity is not fully understood. We postulated that diclofenac-induced embryotoxicity might be related to free oxygen radical damage. Rat embryos were explanted at 9. 5 days gestation and cultured in medium containing various concentrations of diclofenac. The direct effect of diclofenac on embryonic free oxygen radical content was evaluated by measuring the 8-isoprostaglandin F2alpha level. We found that embryos exposed to high concentrations of diclofenac (7. 5 and 15. 0 micro g/ml) had significantly higher levels of 8-isoprostaglandin F2alpha (2. 85 and 3. 50 pg/mm embryonic crown-rump length, respectively) than the control group (1. 73 pg/mm, P<0. 05), while the 8-isoprostaglandin F2alpha level in embryos exposed to low concentration of diclofenac (1. 5 micro g/ml) was 2. 54 pg/mm, which was not significantly different from the control group VSports手机版. Median embryo morphologic score was also lower in the high concentration group compared to the control group (39. 0 versus 44. 0, P<0. 05). These results suggest that diclofenac-induced embryopathy may be related to free oxygen radical damage. .