The nucleotide patterns of the acid soluble extracts of the formed elements of human peripheral blood were determined by high-pressure liquid chromatography. The patterns are remarkably reproducible for each of the respective elements, and the concentration of each major nucleotide present was determined. Erythrocytes are characterized by relatively simple nucleotide patterns with high adenine and very low guanine concentrations. The chromatograms of granulocytes and lymphocytes are difficult to distinguish from one another and demonstrate substantially greater UTP and guanine nucleotide levels than are observed in erythrocytes. The nucleotide patterns of platelets revealed a significantly lower ATP/ADP ratio than did either leukocytes or erythrocytes. The unique potential of this new technique for monitoring changes in nucleotide pools in normal and disease states is discussed.