Six infants with severe life-threatening protracted diarrhoea were treated with loperamide. Steady-state perfusion studies of the jejunum showed that in 2 of them the small intestine was in a net secretory state with respect to water, and in the others this was inferred from the fact that the diarrhoea persisted despite nothing by mouth. Loperamide resulted in a prompt and impressive improvement in the condition of each infant. We conclude that this drug has an important role in the management of protracted diarrhoeal states in some infants who are unresponsive to current treatments, and that its effect is related to its antisecretory action.