Benzenesulfonic acid [(3‐amino‐2,4,6‐trichlorophenyl)methylene] hydrazide, a candidate rodenticide coded as DRC‐4575, was administered by gavage to pregnant female BALB/c mice. Each dose (5.5, 28.0, 42.0, 62.0, and 94.0 mg/kg) was given to one of five groups of ten mice on day 8 of gestation, making a total of five different dose groups on day 8. This same procedure was followed for days 9, 10, 11, 12, and 13. This made a total of 30 dose‐day treatment groups. Six control females were dosed each day. Dam survival to day 18 declined as the dose increased; only 2% of the dams survived at 94 mg/kg. When the surviving females were killed at day 18, no significant differences were found between treatment and control animals in the number or weight of live fetuses, or in the ratio of male to female fetuses. However, the percentage of live fetuses was significantly lower and the number of resorptions was significantly higher for the treated dams at the 62 mg/kg dose level than for the control dams. Skeletal anomalies were limited primarily to unossified phalanges, which were probably related to the lower weights of those fetuses. Slight hydrocephalus occurred infrequently at all dose levels and in the controls, and was not dose‐related. These data indicate that DRC‐4575 would be embryotoxic only at doses of 62 mg/kg or higher and would not be teratogenic.