Cholestyramine 2 g twice daily for 3 days was compared to an equivalent placebo in a randomized double-blind study of infants hospitalized for acute diarrhoea. All the patients received oral rehydration with the WHO solution, and full feedings were reintroduced after 6-10 hours' rehydration. Cholestyramine therapy, initiated at the time of feedings, significantly shortened the duration of watery diarrhoea (0.8 +/- 0.6 vs. 2.3 +/- 1.6 days, p less than 0.005), although it did not significantly reduce the total stool volume. No adverse effects were associated with cholestyramine treatment. It is concluded that diarrhoea patients treated according to the present WHO guidelines may benefit from short adjunct therapy with cholestyramine.