The distribution of birth weights among the infants of 172 Gambian primigravidae who had received chemoprophylaxis with Maloprim (pyrimethamine+dapsone) during pregnancy was compared with that of the infants of 149 primigravidae who had received placebo. Administration of chemoprophylaxis led to a reduction in the prevalence of low birth weight babies and to an increase in the median birth weight. However, these changes were not accompanied by a comparable increase in the prevalence of high birth weight babies. The perinatal mortality rate was lower, although not significantly so, among the babies of women who had received chemoprophylaxis. Thus, no evidence was found to support the view that administration of chemoprophylaxis might increase the risks of delivery by causing cephalo/pelvic disproportion.