Vitamin A supplementation of lactating mothers and of infants at the time of diphtheria-pertussis-tetanus (DPT) and oral polio vaccine (OPV) immunizations have both been suggested as measures to prevent deficiency among infants. This multicenter randomized, double-blind, placebo-controlled trial was conducted in Ghana, India and Peru to determine the effect of maternal vitamin A supplementation on breast milk retinol and of maternal and infant supplementation on infant vitamin A status. Mothers in the intervention group received 60 mg vitamin A (as retinol palmitate) at 18-42 d postpartum; their infants were given 7.5 mg three times, i.e., at 6, 10 and 14 wk of age with DPT and OPV immunizations. Mothers and infants in the comparison group received a placebo. Maternal supplementation resulted in higher breast milk retinol at 2 mo postpartum [difference in means 7.1, 95% confidence interval (CI), 3.4, 10.8 nmol/g fat] and lower proportion of mothers with breast milk retinol < or = 28 nmol/g fat (15.2 vs. 26.6%, 95% CI of difference -16.6, -4.1%). At 6 and 9 mo, maternal supplementation did not affect breast milk retinol or the proportion of mothers with low breast milk retinol. Vitamin A supplementation of the mothers and their infants reduced the proportion of infants with serum retinol < or = 0.7 micro mol/L (30.4 vs. 37%, 95% CI of difference -13.7, 0.6%) and that with low vitamin A stores as indicated by the modified relative dose response (MRDR) > 0.06 (44.2 vs. 52.9%, 95% CI of difference -16.6, -0.9%) at 6 mo. Supplementation had no effect at 9 mo. The beneficial effect of supplementation on breast milk retinol and infants' vitamin A status varied by site. It was greatest in India followed by Ghana and Peru. At the doses used, maternal supplementation improved breast milk retinol status at 2 mo (P < 0.001) and maternal and infant supplementation modestly increased (P = 0.03) infant vitamin A status at 6 mo of age. Additional strategies to improve vitamin A status of 6- to 9-mo-old infants must be considered.