A 12-day nitrogen balance study was designed to determine the protein nutritive value of soy flour and soy protein isolate in human adults. By equalizing the essential amino acid patterns of the flour and the isolate, it was considered possible to measure any difference in nutritive value of the two protein sources. The subjects were 18 healthy women ranging in age from 20 to 25 years. A basal diet provided approximately 1.0 gram of nitrogen and 1400 kilocalories per person per day. The soy protein was incorporated into a low-protein yeast bread providing approximately 500 kilocalories per person per day. The following dietary treatments were used: 1. Basal diet plus 4.0 grams of nitrogen supplied by soy flour. 2. Basal diet plus 4.0 grams of nitrogen supplied by soy isolate. 3. Basal diet plus 3.09 grams of nitrogen supplied by soy isolate. Diet 3 was supplemented with amino acids to match the essential amino acid pattern of the isolate to that of the flour in diet 1. Diet 3 was further supplemented with nonessential nitrogen in the form of ammonium citrate in order to bring the total nitrogen level of the diet up to that of diets 1 and 2, The following data was collected for each dietary treatment: 1} Urinary nitrogen excretion; 2) fecal nitrogen excretion; 3) nitrogen intake based on an analysis of actual food intake. After a 7-day adjustment period to allow subjects to adjust to the low nitrogen intake, nitrogen retention was calculated from data collected during a 5-day experimental period. Nitrogen retentions for the three groups were: flour, -0.06; isolate, -0.30; and supplemented isolate, -0.21 grams of nitrogen per person per day. Analyses of variance showed no treatment effects on urinary or fecal nitrogen excretion or nitrogen retention. It was concluded that, under the conditions of this experiment, soy flour and soy protein isolate are equally well utilized by the human adult. / Ph. D.