The direct demonstration of cereal utilization by 16 healthy 1-month-old infants was achieved by tracing the appearance in breath CO2 of carbon derived from the fed cereal. These oxidation rates were compared with rates obtained from the feeding of glucose and glucose polymers. Fermentation of unabsorbed carbohydrate by the colonic flora was assessed by measurement of breath H2. Stools from four infants were analyzed for the quantity of carbon that originated from the cereal. Oxidation rates were not significantly different (mean = 31.2% of the dose fed). Mean peak hydrogen production was 39.8, 29.1, and 18.6 ppm for cereal, glucose polymers, and glucose, respectively. Cereal carbon was detected in the stools of two infants (3.7% and 13.1% of the ingested load). We conclude that young infants can utilize cereal, although absorption is not always complete. Hydrogen production increases with carbohydrate complexity; participation of colonic bacterial fermentation increases the net absorption of cereal.