1. Glucose absorption, water absorption and dipeptide hydrolase activities have been determined in isolated rat small intestine at 1, 3, 5 and 21 days after a single intraperitoneal injection of 5-fluorouracil.
2. Absorption rates and enzyme activities were elevated 1 day after treatment, but were reduced to 40% of control values at 3 and 5 days. Changes were seen regardless of whether absorption was expressed per unit length or per unit dry weight of intestine.
3. There were highly significant positive correlations between glucose or water absorption rates and peptidase activities, especially in proximal jejunum. The most significant correlation was observed between water absorption rate and jejunal l-Leu-Gly hydrolase activity.
4. Malabsorption may account for some of the gastrointestinal side effects associated with treatment with 5-fluorouracil. Enzyme measurements may be useful as an index of intestinal function.