Ninety 12 month old female rats were used to determine a protein requirement for tissue maintenance. Diets contained 0.84 to 4.69 percent protein and were fed for 28 days. Liver composition, carcass composition and serum protein levels were determined, and a protein requirement level was also predicted. Rats fed 0.84 and 1.86 percent protein had significantly lower serum protein values than a baseline group of rats sacrificed at the beginning of the study. Rats fed the two highest levels of dietary protein had serum protein values which were significantly higher than the baseline group and that of rats fed 2.81 percent protein was not significantly different from that of the baseline group. Rats fed 0.84, 1.86 and 2.81 percent protein had excessive liver fat, indicative of protein deficiency. No group was found to have liver nitrogen values comparable to that of the baseline group. All rats except those fed 0.84 percent protein had significantly more carcass fat than the baseline group. Total carcass nitrogen of rats fed 2.81, 3.77 and 4.69 percent protein were not significantly different from the baseline group indicating a general state of nitrogen equilibrium in these animals. Using linear regression, a protein requirement of 4.07 percent of the diet was predicted. Comparison of this value with other literature values was difficult due to differences in experimental design. It was suggested that in further research of this kind a longer study should be conducted and a concurrent baseline group should be used. / Master of Science