The optimum content of different rice (Oryza sativa) and bean (Vigna unguiculata L.) combinations was studied in Albino rats. The mixture containing 3 g of rice proteins, corresponding to 41g of rice "in natura", and 7 g of bean protein, corresponding to 59 g of bean "in natura", presented the highest protein efficiency ratio and the feed efficiency ratio. Since the limiting amino acid of this mixture was methionine, new assays using varying levels of this amino acid as a supplement were carried out. The PER of normal rats as well as the "plateau" value of previously protein depleted rats were highest when 0.2% methionine was added to the mixture. The net protein utilization (NPU) confirmed these findings. The values attained after the addition of other amino acids were not higher than those attained by the mixture containing 7 g of bean protein and 3 g of rice protein supplemented with 0.2% methionine. The PER and the NPU values came close to those of milk.