AbstractBACKGROUND: Chlorothalonil (2,4,5,6‐tetrachloroisophthalonitril), the nephrotoxic fungicide, was examined for its potential to produce developmental toxicity in mice after oral administration. METHODS: Pregnant ICR (CD‐1) mice were given sublethal doses of 0 (corn oil), 100, 400, and 600 mg/kg/day chlorothalonil by gavage on gestation days (GD) 6–15. RESULTS: Maternal effects in 400 and 600 mg/kg/day dose groups included signs of toxicity such as weakness and depression in the maternal activity, and reduction in body weight and weight gain. No maternal toxicity was apparent in the 100 mg/kg/day dose group. Maternal exposure to chlorothalonil during organogenesis significantly affected the number of live fetuses, early resorption, and mean fetal weight in the 400 and 600 mg/kg/day dose groups. No external, visceral, and skeletal abnormalities were observed among any of the treated groups compared to the control. CONCLUSIONS: On the basis of the present results chlorothalonil can produce clinical signs of toxicity and fetotoxicity without teratogenic effects at 400 and 600 mg/kg/day dose groups. Birth Defects Research (Part B) 77:104–109, 2006. © 2006 Wiley‐Liss, Inc.