When antibody-sensitized Escherichia coli B is treated with complement in the absence of lysozyme, bacterial phospholipids or fragments containing phospholipid appear in the surrounding medium. Almost at the start of the reaction, a little phosphatidylethanolamine (PE) appears in the lipid fraction extracted from the supernatant of the reaction mixture. Later it does not increase greatly in amount but free fatty acids (FFA) and lysophosphatidylethanolamine (LPE) appear and increase gradually. Addition of lysozyme to the reaction mixture changes the amounts of FFA and LPE released, but does not increase the numbers of the spots on a thin layer chromatogram of the lipid fraction of the supernatant. The FFA fraction contains no beta-hydroxymyristic acid from lipid A of the lipopolysaccharide complex.