1. 1. A procedure using column chromatography on Dowex 1 formate with gradient elution by ammonium formate buffer is recommended for the isolation of the water-soluble phosphate compounds of the human erythrocyte. The elution positions of many known compounds of biological interest were determined. 2. 2. Metabolic turnover values for the various water-soluble phosphate compounds present in freshly collected human erythrocytes were measured by the extent of incorporation of 32P and 14C after a brief incubation of blood with 32P i or uniformly 14C-labeled glucose. 3. 3. After incubation of the human erythrocytes with [ 14C 6] glucose, the metabolic intermediates were found to contain 14C in the following order of decreasing concentration: glucose 6-phosphate, fructose 6-phosphate, glucose 1,6-diphosphate > UDPG > fructose 1,6-diphosphate > mannose 1,6-diphosphate > monophosphoglycerate,2,3-diphosphoglycerate. No 14C was found in the ribose portion of any of the ribonucleotides. 4. 4. After incubation of the erythrocytes with 32P i the followign order of decreasing 32P concentration was found in the various phosphate groups of the cell: ATP ( P-3, ATP ( P-2), ADP ( P-2), GTP (≈ P), APPX (≈ P) > glucose 6-phosphate, fructose 6-phosphate > fructose 1,6-diphosphate ( P-1) > triose phosphate > fructose 1,6-diphosphate ( P-6) > glucose 1,6- diphosphate ( P-6) > mannose 1,6-phosphate ( P-6) > glucose 1,6-diphosphate ( P-1) > mannose 1,6-diphosphate ( P-1) > UDPG ( P-2) > mannophosglycerate > 2,3-diphosphoglycerate ( P-2), 2,3-diphosphoglycerate ( P-1). There was no incorporation of 32P into the phosphate attached to ribose in any of the nucleotides. No 32P was found in NAD + of NADP +. No 32P entered into two phosphorus comopunds tentatively identified as inorganic polyphosphates. 5. 5. An individual with polycythemia vera was given 32P i intravenously 10 min before withdrawal of a sample of blood. The erythrocytes exposed to this incubation in vivo with 32P showed the same relative specific activities of their phosphate groups as did human erythrocytes incubasted in vitro.