Mated Charles River CD(trademark)-1 female mice assigned to one control and three treatment groups of 30 animals each were used to determine the developmental toxicity potential of C(sub 9) Aromatic Hydrocarbons. Actual (measured) concentration levels of 100, 500, and 1,500 ppm were received by the animals through whole body inhalation exposure methods once daily for a 6-hour period. Exposure began on day 6 of gestation and was continued to, and included day 15 of gestation. The control group received filtered air on a comparable regimen. Cesarean sections were performed on all females on gestation day 18 and the fetuses were removed for teratologic evaluation. Exposure to the test article elicited developmental toxicity at the 500 and 1,500 ppm levels. Maternal toxicity was elicited at the 1,500 ppm level. In conclusion, the observable effect of C(sub 9) Aromatic Hydrocarbons with respect to toxicity was considered to be 100 ppm when administered by inhalation methods to Charles River CD-(trademark)-1 mice.