A method is descr. for the estimation of the various classes of P compounds present in plant material, and results are given for barley seedlings grown for 5 and 7 days in the dark on solns. with and without phosphate. Phytin was present only in small quantities in the husks (paleae and glumes), endosperms or seedling. Phosphagens of the type of creatine and arginine phosphate were not detected. The inorganic phosphate content of the seedlings was increased by growing the seedlings on culture solns. containing phosphate, but this did not result in an increase of either labile or resistant esters. Inorganic phosphate, labile esters and resistant esters varied with the stage of development. There is little difference between the roots and shoots in regard to labile esters and resistant esters. The shoot has a much larger proportion of lipoid and protein P than the root.