Breath hydrogen (H2) analysis was utilized to determine whether intestinal absorption of carbohydrate might decline with age. Twenty-one healthy subjects (aged 65-89 years, mean age 79.1) and 19 control subjects (aged 20-64 years, mean age 35.6) were fed a meal containing 100 g carbohydrate after an overnight fast. Breath H2 concentrations were analyzed in samples collected intermittently by the end-expiratory technique. A rise in breath H2 concentration of 20 ppm over baseline was considered evidence of intestinal carbohydrate malabsorption: 7 of 21 aged and 0 of 19 control subjects excreted excess H2 (P less than 0.02). Further testing of subjects with meals containing 25-200 g carbohydrate demonstrated a progressive reduction in absorptive capacity with advancing age, while young controls absorbed up to 200 g carbohydrate in a meal. In the group of older subjects carbohydrate malabsorption was not accompanied by clinical determinants of undernutrition. Subtle carbohydrate malabsorption should be considered when evaluating weight loss in old age and in fashioning nutritional programs for the elderly.