The developmental toxicities of 2,4-dinitro-6-(1-methylheptyl)phenyl crotonate and 2,6-dinitro-4-(1-methylheptyl)phenyl crotonate, model isomers of the major active ingredients of technical dinocap, were compared to the known teratogenicity of the technical compound. Individual isomers, both isomers combined, or technical dinocap were administered to pregnant mice on days 7-16 of gestation. Similar to previous studies, technical grade dinocap caused cleft palate and weight deficits in fetuses at term and increased neonatal mortality and abnormal swimming behavior, torticollis, and deficient otolith formation in surviving pups. Neither of the purified isomers exhibited any developmental toxicity when administered under identical conditions. Thus, it is concluded that these isomers are not the active teratogenic component(s) in technical grade dinocap.