This study investigated the nutritive value of Toasted Soy Protein (TSP) when it is incorporated in a basal rice diet. Forty-two male weanling rats were used for a period of 28 days. A total of five diets were fed to five groups of animals having seven animals in each group. An initial group of seven was also included. The composition of the five diets is: 6% rice protein (Diet l); 6% rice protein supplemented with 4% TSP (Diet 2); 6% rice protein supplemented with 4% TSP and 0.15% methionine (Diet 3); 6% rice protein supplemented with 4% casein (Diet 4); and 6% rice protein supplemented with 6.5% TSP. The growth rate for animals fed Diets 2, 3, 4, and 5 is similar, all animals showing an almost uniform weight gain. Supplementation of methionine to Diet 2 did not produce marked increase in weight gain. There is no significant difference in protein efficiency ratio (PER) among animals ingesting Diets 2, 3, 4, and 5. However, an increase of the TSP level from 4% to 6.5% reduced the PER slightly. There was a direct relationship between body weight gain and nitrogen retention as measured by nitrogen balance and liver nitrogen content. The methionine content of the diets and plasma was detennined by microbioassay. The total sulfur-containing amino acid content of Diet 2, i.e.: 0.478% is very close to the requirement of 0.5% for the growing rat. No direct relationship was found between methionine content of the diet and of the plasma. A combination of 6% rice protein supplemented with 4% TSP could be a protein of high quality and this mixture of proteins of plant origins can support and promote good growth of young rats. / Master of Science