Vitamin A deficiency has been postulated to increase childhood mortality, possibly through increasing the severity and case-fatality of infectious diseases like diarrhoea. A clinical trial was conducted to measure the effect of vitamin A therapy on the severity and duration of acute episodes of non-cholera, watery diarrhoea; 83 children with less than 48 h of illness were randomized to receive vitamin A (200,000 IU of retinyl palmitate) orally or placebo during hospitalization at the International Centre for Diarrhoeal Disease Research in Bangladesh. The patients were similar initially with regard to age, nutritional status and severity of diarrhoea prior to admission. No adverse effects of vitamin A were detected. During hospitalization there were no differences between groups in duration of illness or stool output. Thus, vitamin A can be given safely during diarrhoeal illness to augment hepatic reserves and possibly provide a beneficial effect in regard to subsequent episodes of diarrhoea and other infections, but this supplementation should not be expected to have a therapeutic effect on a current episode.