Pregnant Sprague-Dawley rats were exposed to sidestream cigarette smoke (SS) for 6 hr a day, at a concentration of 1 mg/m3 of respirable total suspended particulate material (TSP) on Days 3, 6-10, and 13-17 of pregnancy. Controls were kept in an identical chamber without smoke exposure. The animals were killed on Day 20 of gestation. No differences were found in maternal body weight gain or average daily food consumption between the smoke-exposed and control groups. The numbers of fetuses and of implantation sites per litter were comparable among the groups. None of the pups showed any gross malformations and no difference was found between controls and SS-exposed pups when examined for reduced skeletal ossifications. However, there was a small but significant reduction in mean pup weight. We conclude that intermittent exposure of rats to sidestream cigarette smoke at concentrations severalfold greater than those encountered in smokey public indoor environments causes intrauterine growth retardation.