This study was conducted to quantitate and compare urinary solute transport by ileum and colon in an in vivo rat model. Rates of solute transport were compared by analysis of rate constants for each experiment. Sodium and bicarbonate are secreted while ammonium and chloride are absorbed by both ileum and colon. Potassium is absorbed by ileum and not transported by colon. There is a tendency for water movement into the bowel lumen with both intestinal segments. Quantitatively, the amount of bicarbonate secretion and the increase in intraluminal pH is greater with ileum than colon. There is a net osmolar absorption from ileum but not colon. Hydrogen ion or ammonium absorption accounts for the majority and bicarbonate secretion the minority of the acid load in both ileum and colon. Ammonium appears to be absorbed either along with chloride or in exchange for sodium.