Dichloroacetonitrile (DCAN), a by-product of drinking water disinfection formed by reaction of chlorine with background organic materials, was evaluated for its developmental effects in pregnant Long-Evans rats. Animals were dosed by oral intubation on Gestation Days 6-18 (plug = 0) with 0, 5, 15, 25, or 45 mg/kg/day. Tricaprylin was used as a vehicle. The highest dose tested (45 mg/kg) was lethal in 9% of the dams and caused resorption of the entire litter in 60% of the survivors. Embryolethality averaged 6% per litter at the low dose and 80% at the high dose and was statistically significant at 25 and 45 mg/kg/day. The incidence of soft tissue malformations was dose related and was statistically significant at doses toxic to the dam (45 mg/kg). These anomalies were principally in the cardiovascular (interventricular septal defect, levocardia, and abnormalities of the major vessels) and urogenital (hydronephrosis, rudimentary bladder and kidney, fused ureters, pelvic hernia, cryptorchidism) systems. The frequency of skeletal malformations (fused and cervical ribs) was also dose related and significantly increased at 45 mg/kg. The no-observed-adverse-effect dose for toxicity in pregnant Long-Evans rats was established by statistical analysis to be 15 mg/kg/day.