An investigation of the high-temperature injection (350 degrees C) gas chromatographic behaviour of standards of various classes of phospholipids has elucidated certain characteristic fragments ("tracers") in the pyrogram of each class. Under these conditions of pyrolysis of the phospholipids, a natural mixture of such substances (extracted and purified from cows' milk) has provided evidence for the same "tracers" as for the standards. Analogous results were obtained with a more representative specimen of cows' milk of various breeds grown in areas of different altitudes. The content of fatty acids in phospholipids, tested on each class (separated by means of radial compression high-performance liquid chromatography from polar lipids of milk) appeared to be relatively similar for all the phospholipid classes, and over half the content consisted of unsaturated fatty acids. The major component was delta 9-octadecenoid (oleic) acid.