Application of a recently developed phospholipid saponification procedure to malignant colon or breast tissue produces an unidentified phosphodiester resonance in the 31P nuclear magnetic resonance spectrum which appears to correlate with malignancy. Glycerol phosphodiesters were prepared from a malignant breast tumor by a Folch extraction of the tissue followed by saponification of the resulting phospholipids. These compounds were separated by ion exchange chromatography and the compound responsible for this new resonance was isolated and identified as glycerol 2-phosphoglycerol by high resolution nuclear magnetic resonance spectroscopy. Confirmation of this structure was achieved by chemical synthesis of glycerol 2-phosphoglycerol. Attempts to isolate the phospholipid responsible for this resonance showed that it is not derived from a new class of phospholipids but is most likely an artifact of the new saponification procedure used. Glycerol 2-phosphoglycerol is formed via glycerol 2,3-(cyclic) phosphate derived from phosphatidylcholine followed by reaction with glycerol. Malignant tissue is more prone to produce this compound than is nonmalignant tissue and the differences between these tissue types may be a form of phosphatidylcholine that is present in higher concentrations in malignant tumor membranes than in those of normal tissue.