While there is evidence that human perinatal exposure to environmental tobacco smoke (ETS) can result in an increased risk of respiratory disorders and sudden infant death syndrome, evidence linking ETS exposure to neurodevelopmental handicaps is suggestive but less compelling. We previously noted that postnatal ETS exposure, rather than prenatal exposure, resulted in reduced concentration of hindbrain DNA and increased protein/DNA ratio when rat brain tissue was studied at 9 weeks postnatal age. We have now evaluated the effects of ETS exposure during pregnancy on brain development by assaying brain tissue at term. ETS exposure had no detectable effects on regional brain concentrations of DNA, protein and cholesterol or on protein/DNA and cholesterol/DNA ratios. While ETS exposure during pregnancy also had no detectable effects on the weights of the individual fetuses or on the weights of various organs, certain regions of the fetal skeleton demonstrated accelerated ossification. The findings of this study are contrasted to the developmental effects of both nicotine and ETS in Rhesus macaques. Additional studies designed specifically to assess the risk of prenatal ETS exposure on brain development in non-human primates and other precocial species are warranted.