The objective of this study was to investigate the mechanisms involved in intestinal absorption of fructose. The results indicate that adult rats readily absorbed 0.4 g of fructose, an amount equivalent to 1.4-1.6 g fructose/kg body wt. Acute malabsorption of fructose occurred with doses greater than 0.6 g (2.1-2.4 g/kg body wt). Continued exposure to dietary fructose resulted in a decrease in the evidence of colonic fermentation. Glucose or galactose administered with fructose enhanced the absorption of fructose. The greatest absorption was observed when equal amounts of fructose and glucose were given simultaneously. If glucose was ingested as a polymer (starch or dextrin), the stimulatory effect was dependent on the digestibility of the polymer. Sucrose given with the fructose and glucose diminished the absorption of fructose. Acarbazone, a specific inhibitor of alpha-glucosidases, including sucrase, also inhibited the facilitating effect of glucose and galactose in absorption of fructose. These results give evidence for joint absorption of the two monosaccharides, fructose and glucose.