A double-blind, randomized, controlled clinical trial was conducted on 80 malnourished children with acute dehydrating diarrhoea to evaluate the efficacy of oral supplementation of zinc as an adjunct therapy to oral rehydration solution (ORS). After decoding it was observed that 44 children received zinc sulphate (177 mg/kg/day in three divided doses equivalent to 40 mg elemental zinc) in a syrup form and 36 children received only syrup placebo. Clinical parameters and microbiological findings of stool samples were comparable in the two groups at the time of enrollment. All the children (100 per cent) in the zinc supplemented group and 32 (89 per cent) children in the placebo group recovered within 5 days of hospitalization (p = 0.04). The zinc supplemented group had a significantly shorter duration of diarrhoea (70.4 +/- 10.0 vs. 103.4 +/- 17.1 h; p = 0.0001), passed less liquid stool (1.5 +/- 0.7 vs. 2.4 +/- 0.7kg; p=0.0001), consumed less oral rehydration solution (2.5 +/- 1.0 vs. 3.6 +/- 0.8 litre; p = 0.0001) and other liquids (867.0 +/- 466.1 vs. 1354.7 +/- 675.6 ml; p = 0.0001) as compared to the placebo group. Our findings suggest that zinc supplementation as an adjunct therapy to ORS has beneficial effects on the clinical course of dehydrating acute diarrhoea.