146 infants with cow's milk protein intolerance (CMPI), defined as two positive elimination/challenge tests with cow's milk, after exclusion of lactose intolerance were selected for a prospective study. A cow's milk free diet consisting of a protein hydrolysate (Pregomin [Milupa] is a protein hydrolysate, containing proteins of animal (collagen) and vegetable (soy) origin, or a soya bean infant formula (Nutrisoy, Nutricia) was given. 69/151 infants were fed a soy bean-based formula. 15/69 (20.3%) were intolerant of soy proteins. 4/82 infants (4,9%) became intolerant for the protein hydrolysate. Infants with soy or proteinintolerance were challenged to confirm the adverse reaction.

After a mean of 16 weeks 70/82 infants on a protein hydrolysate formula received soy and only 3 of these infants (4.3%) were found intolerant of soy proteins.

We conclude that soy intolerance is frequent in infants with CMPI and after a 2-3 month period of receiving a protein hydrolysate formula, soy intolerance has been reduced to only 4.3%.