[3H]Trioleyl glycerol (TO) and [14C]vitamin D3 were perfused intraduodenally for 5 hr in aged (19-21 months) and young adult (4-5 months) Sprague-Dawley rats. The rate of intestinal uptake from the gastrointestinal lumen and transport into the body of these lipids were decreased in the aged animals. Since the distribution of TO lipolytic products in the lumen was unchanged, reduced intestinal uptake rate probably occurred at the mucosal membrane. Furthermore, in the aged rats, the rate of transintestinal transport of both trioleyl glycerol and vitamin D3 was impaired. No evidence for impaired mucosal TO reesterification or for accumulation of vitamin D3 metabolites was found, suggesting that intestinal lipid accumulation resulted from a defect in lipoprotein assembly or in discharge from the mucosal cell. Impaired absorption of lipids may contribute to malnutrition and osteopenia of advancing age.