Abstract: The author attempts to utilize the molybdovanadophosphoric (MVP) acid method for the colorimetric determination of inorganic phosphorus in blood. This method is applicable to the determination of 0.05-0.30 mg of phosphorus in 25ml of solution. The sensitivity is up to 0.01 mg P/25ml. The MVP acid (yellow complex) is more stable and reproducible than the molybdenum-blue complex of phosphate. The proposed method is as follows: Accurately transfer 2 ml of blood sample to a test tube (about 15 ml capacity), 8 ml of 10% trichloroacetic acid is added. After mixing, the sample is allowed to stand for 10 minutes, filter. Transfer 5 ml of the filtrate (protein-free blood filtrate) into a 25 ml volumetric flask, add 2 ml of mixed reagent (molybdic and vanadic acids), then dilute to the mark with distilled water and mix. After 5 minutes, determine the extinction of the solution in a photoelectric colormeter, using a violet filter (BG 12). Reagents are used as a blank.