IT is generally assumed that when phosphocreatine is hydrolysed either enzymatically or spontaneously, the end products are creatine and phosphoric acid. This, however, is not always found to be the case. When phosphocreatine is hydrolysed at 38° in saturated picric acid, about 10 percent of the substance is converted into creatinine (Fig. 1.). Under these conditions, creatine is not transformed into creatinine. Obviously phosphocreatine has a certain spontaneous tendency to ring formation. If heated to 100° either in picric acid or hydrochloric acid, there is a rapid formation of creatinine, followed by a linear increase due to the reaction creatine - creatinine (Fig. 2.). If the two curves are subtracted, a curve of much the same appearance as Fig. 1 results. Whether picric or hydrochloric acid is used for hydrolysis is of no importance.