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What appears to be a new class of phospholipids has been isolated from dog brain in the form of complexes with a substituted phthalanilide. The complexes were extracted by chloroform-methanol and purified by countercurrent distribution in solvent systems containing water, chloroform, methanol, and Freon 113. The binding of the phthalanilide congener to lipids has some ionic character. Cations such as H(+) or Ca(++) displaced the phthalanilide from its lipid complex. The pH for 50% displacement acid was about 3.8 and was independent of the purity of the complex. Thin-layer chromatography of the lipid yielded four subfractions of lipid, three of which were ninhydrin-positive and all of which yielded a group of unidentified ninhydrin-positive components on hydrolysis. Each lipid subfraction contained nitrogen, phosphorus, fatty acids, and glycerol but in different ratios. Of the known phospholipids containing nitrogen, none matches the composition and behavior of the lipids isolated as phthalanilide complexes. We have therefore concluded that the phthalanilides bind to a new class of phospholipids characterized by a high content of unidentified ninhydrin-positive components.