The protein nutritional quality of foods has become an important factor to food processors with the advent of nutritional labeling regulations for foods. Then, as is true today, the officially approved assay for protein nutritional quality was the rat based protein efficiency ratio(PER) bioassay. The PER bioassay requires a minimum of 28 days to performe, and is therefore not applicable to routine quality assurance use by the food industry. Within the past ten years there has been a research emphasis placed on the development of rapid, inexpensive, biological and/or chemical based assays for protein nutritional quality. It was hoped that if a rapid assay could be developed and thoroughly tested, it could be used in lieu of the PER bioassay in the day-to-day quality assurance screening of food ingredients and products. The rapid assays developed in the hope of attaining this goal have been based on microorganisms, proteolytic enzymes, and amino acid profiles, as well as combinations of the above. In this review, it will be described and briefly discussed many of procedures which had contributed conceptually as well as practically to the development of in vitro methods for the evaluation of protein quality. Special emphasis will be placed on the C-PER(computed protein efficiency ratio) assay which combines data from in vitro protease digestion and amino acid composition to predict protein nutritional quality designed by Satterlee et al. (1980), and the DC-PER(discriminant computed PER) which is a method of estimating protein quality based on rat assay and in vitro digestibility obtained using solely essential amino acid data will be also introduced.