The identity of a number of phosphorus-containing metabolites present in Synechocystis sp. PCC 6308 has been confirmed by P-31 NMR spectroscopy. The presence of D-ribulose 1,5-bisphosphate (RuBP); DL-glyceraldehyde 3-phosphate (GlyP); D(-) 3-phosphoglyceric acid (3PGA); D-ribulose 5-phosphate (Ru5P); 6-phosphogluconic acid (6PGA); phosphoenolpyruvate (PEP); inorganic phosphate (Pi); uridine diphosphoglucose (UDPG); ADP and ATP were demonstrated by the pH dependence of their P-31 NMR chemical shifts in spectra of perchloric acid cell extracts. Intracellular pH of cells was determined to be 7.5-7.7.