Small intestinal perfusion studies have been carried out in animals to evaluate the role of the individual constituents of oral rehydration solution (ORS), in order to draw some conclusions relating to the optimal composition of ORS. Two commercially available ORS, Dioralyte and Rehidrat have also been compared to the World Health Organisation (WHO) standard solution. Maximum rate of water absorption occurred with the WHO solution and least with Rehidrat. The findings of the perfusion studies suggest that in the normal small intestine, optimal water absorption occurs from a solution containing 60 mmol/l of sodium and 80-120 mmol/l of glucose. The addition of bicarbonate and citrate at concentrations present in ORS does not appear to have a significant effect on water absorption. The addition of glycine and diglycine to the standard ORS reduced the net rate of absorption of sodium and water, probably because of the effect of increased osmoality.