The nutritional composition of milk obtained during the first month postpartum from 33 mothers delivering preterm and 18 mothers delivering at term was determined. Milk produced by mothers delivering preterm contained significantly higher concentrations of protein, sodium, and chloride, and significantly lower concentrations of lactose than milk produced by mothers delivering at term. The caloric concentration of milk produced by the two groups of mothers was similar, as were the concentrations of potassium, calcium, phosphorus, and magnesium. PT milk appears to approximate more closely the nutritional needs of the preterm infant than does other breast milk.