ABSTRACT The present study was undertaken to examine early postnatal mortality in rat pups following exposure to butyl benzyl phthalate (BBP) during pregnancy. Seventeen pregnant rats were given 750 mg/kg bw/day of BBP by oral gavage on gestation days 13, 14, and 15, and the volume of each dose was adjusted to 5 ml/kg body weight. Four rats were given olive oil only and served as control. Natural birth was allowed to take place. One hundred and eighty-three pups were born to the experimental rats and 46 pups to the control group. Close observation of the newborn pups during the first 3 h of life revealed that all the pups in both the control and experimental groups were born alive. Only six pups from the experimental group (3.2%) died within this time period. These and four control pups were fixed and decalcified. Histological examination of the thoracic cavity of the newborn rats in both groups revealed no differences in the position or size of any of the heart chambers, ductus arteriosus, or great vessels. However, the lungs of the six experimental pups that died showed athelectasia and bronchi dilatation. The results therefore suggest that exposure to BBP of rats during pregnancy does not produce significant postnatal mortality in their offspring.