BACKGROUND Cow milk protein intolerance (CMPI) is characterized by a wide range of symptoms and signs affecting the gastro-intestinal tract, the respiratory system and the skin. A better definition, a stricter application of diagnostic criteria and critical evaluation of certain immunologic correlates can contribute to a better understanding and preventive treatment of this entity. METHODS Two hundred-seventeen infants with CMPI seen between January 1980 and December 1993 were included in the study. They were classified into two groups: 1) acute reaginic CMPI (type I): 125 infants and 2) CMP enteropathy or colitis (type III or IV): 92 infants, according to classical diagnostic criteria. Careful investigation concerning the type of milk feeding (breast or artificial) proposed prior to clinical manifestations was performed. RESULTS Among the 125 infants (aged 3 to 20 weeks) with acute reaginic CMPI, 121 (97%) had been breast-fed with a sudden weaning; 30 of these infants had also received one to three formula bottles during the first 3 days of life and 14 certainly had not received such formula bottles. Among the 92 infants with CMPI, type III or IV, 33 (38%) had been exclusively breast-fed, a figure quite similar to the breast feeding incidence in our region. CONCLUSIONS These results clearly show the importance of breast-feeding in the personal history of CMPI. Acute reaginic type of CMPI is favored by early ingestion of formula bottles in breast-fed infants and by early sudden weaning. Hypoallergenic formula in five cases was unable to protect infants against further allergic manifestation.