The lactose, glucose, and galactose content in various fermented milk products was studied by enzymatic methods. Lactose was decreased in all fermented products. After 11 days storage of yogurt the lactose content decreased to about 2.3 g/100 compared to 4.8 g/100 g in nonfermented milk. During the same period, galactose content increased from traces in milk to 1.3 g/100 g in yogurt. Results were similar with acidophilus and bifidus milk. Buttermilk, kefir, and ropy milk showed 26, 30, and 20% decreases in lactose content. Eight lactose intolerant individuals showed symptoms of abdominal distress and diarrhea following consumption of 500 ml of low fat milk whereas ingestion of the same quantity of yogurt or acidophilus milk did not result in any symptoms. Fermented milk products should be considered in formulating diets for lactose-intolerant subjects.