Six normal full-term infants were fed human milk during all of the first 6 months of life and three normal full-term infants were fed human milk during portions of that period. Data are presented concerning growth in length and weight. The mean concentration of total protein in the serum was 5.2 gm/100 ml and that of urea nitrogen was 6.3 mg/100 ml. Data from 74 nitrogen balance studies of the nine infants are presented. The mean volume of intake of pasteurized human milk during the balance periods performed in the first 1½ months of life was 218 ml/kg/day, decreasing to 140 ml/kg/ day between 4½ and 6 months of age. Assuming a mean concentration of 67 cal/100 ml of the pooled human milk, the mean caloric intake of the infants during the first 1½ months of life was 147 cal/kg/day, decreasing to a mean intake of 94 cal/kg/day between 4½ and 6 months of age. The mean intake of protein during the first 1½ months of life was 2.4 gm/kg/day, decreasing to 1.5 gm/kg/day between 4½ and 6 months of age. The mean retention of nitrogen at 1 month of age (calculated from the regression equation) was 180 mg/kg/day, gradually decreasing to 47 mg/kg/day by 6 months of age. These retentions are considerably less than those reported for infants receiving the higher intakes of protein (generally more than 3.5 gm/kg/day) provided by many formulas of cow's milk. The mean gain in weight for each gram of nitrogen retained by the infants was 42.1 gm.