A method for measuring protein using the Folin phenol reagent is described. The method involves alkaline copper treatment followed by reduction of the Folin reagent. The procedure is applicable to proteins in solution or after precipitation with acids or other agents. The method allows for the determination of as little as 0.2 γ of protein. The reagent is highly sensitive and simple to use, making it suitable for various biochemical applications. However, the color produced varies with different proteins, and the reaction is not strictly proportional to concentration. The method is particularly useful for measuring small amounts of protein, mixed tissue proteins, and proteins in diluted or colored solutions. The procedure involves mixing the sample with alkaline copper reagent, allowing it to stand, and then adding the Folin reagent. The color is measured using a spectrophotometer. The method is also applicable to microanalysis, where small volumes of samples and reagents are used. The method has certain advantages, including high sensitivity and simplicity, but it is less specific than other methods. The method is recommended for a variety of biochemical purposes, including the measurement of proteins in enzyme fractionations, mixed tissue proteins, and large numbers of similar protein samples. The method is not suitable for measuring free amino acids, as they produce more color than proteins. The method is also not suitable for measuring proteins that are highly denatured or that contain other nitrogen-containing substances. The method is described in detail, including the preparation of reagents, the procedure for measuring proteins in solution or after precipitation, and the procedure for microanalysis. The method is also discussed in terms of its advantages and disadvantages, and its applications in biochemical research. The method is recommended for use in a variety of biochemical applications, including the measurement of proteins in serum, antigen-antibody precipitates, and insulin. The method is also discussed in terms of its limitations, including the variability in color production and the need for careful handling of the reagents. The method is described in detail, including the preparation of reagents, the procedure for measuring proteins in solution or after precipitation, and the procedure for microanalysis. The method is also discussed in terms of its advantages and disadvantages, and its applications in biochemical research.A method for measuring protein using the Folin phenol reagent is described. The method involves alkaline copper treatment followed by reduction of the Folin reagent. The procedure is applicable to proteins in solution or after precipitation with acids or other agents. The method allows for the determination of as little as 0.2 γ of protein. The reagent is highly sensitive and simple to use, making it suitable for various biochemical applications. However, the color produced varies with different proteins, and the reaction is not strictly proportional to concentration. The method is particularly useful for measuring small amounts of protein, mixed tissue proteins, and proteins in diluted or colored solutions. The procedure involves mixing the sample with alkaline copper reagent, allowing it to stand, and then adding the Folin reagent. The color is measured using a spectrophotometer. The method is also applicable to microanalysis, where small volumes of samples and reagents are used. The method has certain advantages, including high sensitivity and simplicity, but it is less specific than other methods. The method is recommended for a variety of biochemical purposes, including the measurement of proteins in enzyme fractionations, mixed tissue proteins, and large numbers of similar protein samples. The method is not suitable for measuring free amino acids, as they produce more color than proteins. The method is also not suitable for measuring proteins that are highly denatured or that contain other nitrogen-containing substances. The method is described in detail, including the preparation of reagents, the procedure for measuring proteins in solution or after precipitation, and the procedure for microanalysis. The method is also discussed in terms of its advantages and disadvantages, and its applications in biochemical research. The method is recommended for use in a variety of biochemical applications, including the measurement of proteins in serum, antigen-antibody precipitates, and insulin. The method is also discussed in terms of its limitations, including the variability in color production and the need for careful handling of the reagents. The method is described in detail, including the preparation of reagents, the procedure for measuring proteins in solution or after precipitation, and the procedure for microanalysis. The method is also discussed in terms of its advantages and disadvantages, and its applications in biochemical research.