1 079 of 1 548 newborn infants were followed during their first year. 328 were prospectively contacted once a month. 751 were followed up at child welfare clinics. Altogether 20 were diagnosed as being cow's milk protein intolerant (1.9%). Symptoms from the gastrointestinal tract and the skin predominated. Only 2 had respiratory symptoms. Ten had their symptoms within one week after the introduction of cow's milk, 3 of them at their first cow's milk-containing meal. A further 4 already had symptoms when fed only human milk. The others (6 infants) showed symptoms after more than one week on a cow's milk containing diet. Before 2 years of age, 13 had recovered. Twelve of the cow's milk protein intolerant infants also showed adverse reactions to other foods, soy-protein intolerance being the most common (7 infants). A family history of allergy was found in 35% (116) of the 328 infants and in 70% (14) of those with cow's milk protein intolerance.