Structures of phosphatidylcholines having an oxidatively shortened fatty acyl group resemble that of the platelet-activating factor (PAF), a chemical mediator of inflammation, and therefore they are classified as PAF-like lipids. Gas chromatography-mass spectrometry has been utilized for analysis of the class, subclass and molecular species compositions of PAF-like lipids, providing usefel informations on mechanisms of their formation. Gas chromatography-mass spectrometry was also found to be useful for the determination of lysophosphatidic acid, a growth factor in animal plasma, and clarification of mechanisms of its formation.