Milks based on isolated soy protein enriched with dl-methionine are rapidly coming into common use in pediatric practice. The biological value of its protein has been measured at critical levels in the initial therapy of malnourished infants and children and during convalescence. Absorption and retention of nitrogen, as well as growth rates, were equivalent to those from modified cow's milk. Normal serum albumin levels were achieved and maintained, as were levels of fasting plasma amino acids, both indicative of dietary protein adequacy. These results confirm the enormous potential of isolated soy protein in human nutrition, particularly in the diet of those intolerant of milk proteins or lactose.