1. A group of five male infants who received an average nitrogen intake of 98 mgm./kg./day, derived from cow's milk protein, retained an average of -2.0 mgm./ kg./day. Small positive balances were achieved at intakes of 110 mgm./kg./day in two subjects. An intake of 100 mgm./kg./ day in two subjects resulted in one instance of nitrogen equilibrium and one of negative nitrogen balance. In the subject given the lowest nitrogen intake, 70 mgm./kg./day a negative nitrogen balance was encountered. These data suggest that the lower limit of nitrogen intake for equilibrium in infants under the experimental conditions reported here is approximately 110 mgm./kg./day.

2. Two of these subjects received gelatin supplements providing 120 mgm. N/ kg./day, and responded with increased nitrogen retentions of 50 and 60 mgm. N/ kg./day.

3. Retention of the gelatin supplements was not further increased in either subject by the administration of 300 µg. of vitamin B12, and 200-300 mgm. of aureomycin daily.

4. The provision of a protein which does not contain all of the essential amino acids, as a supplement to protein of good biological quality permits real augmentation of nitrogen retention.

5. Certain implications of the data in regard to the nutritional value of sub-optimal intakes of nitrogen and total calories have been discussed.

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