A simple method is described for the determination of serum glycerophosphatides, with the exception of lyso-phosphatide. Two determinations are necessary. The usual "triglyceride" determination is performed on native serum, and a further determination is performed after incubation of the serum with phospholipase C. Glycerophosphatides are hydrolysed to diglycerides and phosphorylcholine by phospholipase C. The resulting diglycerides are determined in addition to the mono-, di-, triglycerides and free glycerol of the native serum. The difference between the two glyceride determinations corresponds to the concentration of glycerophosphatides. Involvement of glycerophosphatides in blood coagulation and their increased levels in certain liver illnesses are two reasons for the importance of the present method. Compared with the usual method of measuring phospholipid phosphorus, the present method involves considerably less work, and, as a fully enzymatic method, it has a higher specificity.