Application is made of the isotopic dilution method to phosphorus analysis when this element is present at the level of ppm in uranium compounds. The efficiency of the method is checked by snalysis of samples of sodium phosphate with known amounts of phosphorus, as well as by analysis of samples of uranium with known amounts of phosphorus. The experimental method is described. The method is being used to analyze various batches of atomically pure uranium produced by the Uranium Pilot Plant of the Instituto de Energia Atomica. (auth)