Vitamin A administration in children reduces the incidence of severe diarrhea during the subsequent few months. We therefore examined the effect of treatment with vitamin A during acute diarrhea on the episode duration and severity. In a double-blind controlled field trial, 900 children 1 to 5 y of age with acute diarrhea of < or = 7 d duration were randomly assigned to receive vitamin A (60 mg) or a placebo. Children were followed up at home every alternate day until they recovered from the diarrheal episode. In all study children, those treated with vitamin A had a significantly lower risk of persistent diarrhea [odds ratio (OR) 0.30, 95% confidence interval (CI) 0.07-0.97], but there was no effect on the mean diarrheal duration or the mean stool frequency, in the subgroup of children who were not breast-fed, the mean diarrheal duration [ratio of geometric means (GM) 0.84, 95% CI 0.72-0.97], mean number of stools passed after the intervention (ratio of GM 0.73, 95% CI 0.56-0.95), the proportion of episodes lasting > or = 14 d (P = 0.002) and the percentage of children who passed watery stools on any study day (OR 0.40, 95% CI 0.21-0.77) were significantly lower in those treated with vitamin A. We conclude that administration of vitamin A during acute diarrhea may reduce the severity of the episode and the risk of persistent diarrhea in non-breast-fed children. Similar benefit was not seen in breast-fed children.