Many infant formulas are available as alternatives to breast-feeding. These formulas are necessary and valuable resources in the nutriture of infants, but it is important to evaluate their use and efficacy periodically. Soybean preparations were suggested as a milk substitute by Hill and Stuart1 in 1929. Since then, the use of these products has expanded appreciably, and they are used for an estimated 10% to 15% of all formula-fed infants. This increase in use has prompted examination of the following critical issues about the indications for use of soy-protein formulas in infants. (1) Are soy-protein formulas an adequate nutritional substitute for cow's milk-based formulas in full-term infants? (2) Is it appropriate to recommend soy-protein formulas to provide a lactose-free formula, or are there better alternatives? (3) Are soy-protein formulas ever indicated for use in premature infants? (4) What is the evidence for and against the use of soy-protein formulas in the management of cow's milkprotein allergy? (5) What is the role of soy-protein formulas in prophylaxis of allergic disease? (6) What is the evidence for and against the use of soy-protein formulas in the management of "colic"? Examination of these issues will hopefully, provide a more clear-cut basis for decisions regarding the use of soy-protein formulas and updated recommendations for the role of soy-protein formulas in feeding human infants. COMPOSITION OF SOY-PROTEIN FORMULAS Soy-protein formulas, although different in carbohydrate and protein source, are similar in composition to cow's milk-protein formulas following the American Academy of Pediatrics, Committee on Nutrition, 1976 recommendations for nutrient levels in infant formulas.2