Mothers' milk, fortified daily with skim and cream components derived from mature donor human milk, was fed fresh during the first 2 postnatal months to 18 (group FMM) healthy, very low birth weight (VLBW) infants. Following the same feeding protocol, 16 additional VLBW infants were fed commercial formula that had a similar range of energy and nitrogen. Infants were evaluated for growth, metabolizable energy, balances of nitrogen and fat, and biochemical markers of nutritional status. Growth measurements from birth to 1800 gm were similar in the two groups. Nutritional balance was performed at approximately 2.5 (first study period) and 6 (second study period) weeks. Metabolizable energy (average 109 kcal/kg/day) was similar in both groups and met theoretical needs of the growing VLBW infant. Apparent nitrogen retention was similar and equivalent to estimates of intrauterine nitrogen accretion (approximately 325 mg/kg/day). Fat absorption increased from the first (70% of intake) to the second study (80% of intake) and was similar in both groups. Serum values for albumin, total protein, prealbumin, hemoglobin, and creatinine were also similar, and declined with increases in postnatal age. Significant differences were observed between feeding groups for serum phosphorus and calcium. These results indicate that healthy VLBW infants maintain adequate growth and macronutrient balance for the first 2 months postnatally when fed mothers' milk fortified with additional skim and cream components.