THE isolation and purification by Bailey and Webb1 of a phosphatase, which acts specifically on inorganic pyrophosphate, makes probable the occurrence in baker's yeast of this compound as a natural meta-bolite. That inorganic pyrophosphate may be accumulated under certain conditions in baker's yeast is revealed by the experiments described below. Studying the mechanism of the inhibition of the respiration caused by the lithium ion in baker's yeast, we had observed the accumulation of an easily hydrolysable phosphate compound. This was prepared in the following way. In 5 l of 0.080 M sodium potassium succinate buffer of pH 5.0, the [K] of which was 1/10 of its total alkaline ion concentration, sufficient lithium chloride was dissolved as to make the solution 0.40 M with respect to lithium. Tn this solution 170 gm. fresh yeast was suspended and a powerful stream of oxygen was bubbled through the mixture (temperature, 20° C.). After one hour, the lithium now being in equilibrium with the interior of the cells, 5.4 gm. of glucose was stirred into the mixture and the aeration continued for another thirty minutes. At the end of this time the sample was fixed by addition of perchloric acid. The yeast cells were extracted at 0° C, the pH of the liquid raised to 8 and the cells centrifuged off. The clear extract was treated with excess barium chloride. The precipitate was centrifuged down, dissolved in normal hydrochloric acid and the clear solution again precipitated with barium chloride at pH 4.5. The barium salt thus obtained was purified by repeated precipitation.