Some applications to biological samples of a method for the separation and the quantitative analysis of phospholipids by high performance liquid chromatography (HPLC) and light scattering mass detection are described. Results obtained in the determination of phospholipid classes from rat tissues such as liver, heart and kidney have been compared with data from the literature. The method has been applied to the evaluation of phospholipids in human low-density lipoproteins (LDL), about which little is known. The procedure is also suitable for a rapid and reliable assay of the water-soluble phospholipase A2 activity; the relationship between the aggregation state of substrate phospholipids (mixed micelles, multilamellar and unilamellar vesicles) and the enzyme activity has been studied.