The osmotic effect of unabsorbed glucose on intestinal secretion of water and electrolytes was investigated by jejunal perfusion in eight infants ranging from 2 to 17 months of age. All infants had or were recovering from acquired monosaccharide intolerance. Isocaloric solutions of glucose and glucose polymer containing 1% polyethylene glycol as a nonabsorbable marker were tested. The osmolalities of the glucose polymer solutions were 1/3 to 1/6 that of the glucose. No major differences were noted in carbohydrate absorption whereas mean water flux changed from secretion of 0.37 ml/min to absorption of 0.023 ml/min when glucose was replaced by glucose polymer. Sodium and potassium flux followed the same pattern. The results of this study indicate that the increased intestinal secretion in acquired monosaccharide intolerance may be a function of osmolar load in the presence of a reduced absorptive capacity.