We evaluated the safety and efficacy of 3 oral doses of 50,000 IU vitamin A at monthly intervals in predominantly breastfed infants from poor urban Bangladesh aged 6 to 17 weeks along with DPT and oral polio vaccines in a randomised double-masked controlled trial. Ninety-seven infants received vitamin A and 103 received placebo. Initial fasting serum retinol concentrations were very low in most infants (52% < 10 mu g/dl and 74% < 15 mu g/dl) which improved in both groups but was still less than 15 mu g/dl in 30% of those who received vitamin A. Nine infants in the vitamin A group and 2 in the placebo group had bulged fontanelle after the second and/or third dose (RR = 4.78, 95% CI 1.06-21.54, P < 0.025) which resolved in 48 hours. In conclusion young infants from a deprived urban community in Bangladesh were deficient in vitamin A; a large proportion remained deficient even after three large doses of vitamin A. In spite of deficiency, bulged fontanelle, an apparent toxic manifestation, occurred in 9.3% with this dosage schedule of vitamin A. Alternative and/or complementary approaches e.g. maternal supplementation are needed to prevent vitamin A deficiency in under 6 month infants in developing countries. Copyright (C) 1997 Elsevier Science Inc.