A simple and rapid method for the determination of ATP, ADP, AMP, NADP⁺, NAD⁺, NADPH, and NADH in human erythrocytes is described. A single-step extraction procedure employing alkaline medium and CF 50A Amicon ultrafiltration membranes allows a simultaneous and total recovery of the compounds of interest. Analysis is performed by reverse-phase high-performance liquid chromatography on a 5-μm Supelcosil LC-18 column and uv detection. Extraction and analysis require about 30 min. Levels of adenine and pyridine nucleotides in normal adults are also presented.