The molybdate methods were shown to have limited application for estimation of inorganic phosphate (P1) in the samples containing phosphocarbohydrates. The definite concentrations of phosphosugars caused the formation of blue molybdenic color. The ascertained critical concentration of Pi and the maximal content of phosphocarbohydrates in the solution studied enabled to estimate P1 in the presence of phosphorus esters of carbohydrates with use of the specific, sensitive and simple method.