Dissolved organic phosphorus may be determined, even in highly coloured alkaline soil extracts, by the application of photoelectric colorimetry to the ceruleomolybdate colour reaction of phosphate ions. Total organic phosphorus may be extracted from soil with 4 N hydrochloric acid followed by treatment of the residue with 3 N ammonium hydroxide. Inorganic phosphorus is determined by direct colorimetry in the acid extract and in the acidified alkaline extract. Total phosphorus is determined similarly in each extract after ignition. The difference between total and inorganic phosphorus is equivalent to the organically combined phosphorus content of the soil sample.The soil organic phosphorus was found to be stable under these treatments. A considerable proportion of the organic phosphorus is extracted by acid, and the total soil phosphorus is almost completely extracted by the two treatments with 4 N hydrochloric acid and 3 N ammonium hydroxide.