Fifty patients of grade III & IV malnutrition with diarrhoeal dehydration were rehydrated using the WHO recommended ORS. Serum sodium and potassium levels were estimated at admission and 24 hours later. Forty seven patients were successfully rehydrated orally. In 7 patients the level of dehydration at initial assessment was overestimated. Periorbital edema developed in 25.5% of the patients rehydrated. No patient had cardiac failure or convulsions during therapy. Though persistent hyponatremia and hypokalemia were found in 10.6% and 19.15% cases respectively after rehydration, the incidence decreased as compared to the pre-hydration levels and was comparable to that found in malnourished children without diarrhea who served as controls in the present study. Oral rehydration was discontinued in three patients due to development of excessive vomiting in one case and paralytic ileus in two. Thus WHO ORS can be used safely in children with severe malnutrition but constant monitoring is required.