Questions of infant nutrition can often be answered by metabolic balance studies or by studies of food intake and growth. The methods used by the authors for these approaches are described and an example of each is given. Balance studies demonstrated that lactose was more effective than a corn starch hydrolysate in promoting absorption of calcium, magnesium and manganese. A study of food intake and growth provided convincing evidence of the ability of infants to digest starch adequately after 6 weeks of age. There was a suggestion that some infants less than 6 weeks of age had limited ability to digest starch.