The American Academy of Pediatrics is committed to breastfeeding as the ideal source of nutrition for infants. For those infants who are formula-fed, either as a supplement to breastfeeding or exclusively during their infancy, it is common practice for pediatricians to change the formula when symptoms of intolerance occur. Decisions about when the formula should be changed and which formula should be used vary significantly, however, among pediatric practitioners. This statement clarifies some of these issues as they relate to protein hypersensitivity (protein allergy), one of the causes of adverse reactions to feeding during infancy.