Lactose digestion from and tolerance to lactose-containing beverages consumed with food was evaluated in 12 lactase-deficient subjects by breath-hydrogen techniques. Peak hydrogen production after a milk-based food supplement was delayed 2 h as compared with a lactose solution. Addition of a breakfast meal further delayed peak hydrogen production by 1 h. Hydrogen production was significantly lower (p less than 0.03) for the first 4 h after ingestion of the supplement plus meal compared with the supplement alone. Nine subjects experienced intolerance symptoms after consumption of the supplement alone but only three experienced them after consumption of the meal plus supplement. Severity of symptoms was significantly reduced with the ingestion of the supplement compared with an equal lactose load and was further reduced with the consumption of food, presumably due to delayed gastric emptying. Thus, lactose malabsorbers should consume food simultaneously with lactose-containing beverages to reduce intolerance symptoms.