The action of exogenous phospholipases on Escherichia coli has been examined. Cells harvested in late log phase were found to be completely resistant to the action of phospholipases A2 and C. Treatment of cells with Tris and EDTA was required to make the phospholipids in the cell accessible to these phospholipases. Phospholipase A2 hydrolyzed mainly phosphatidylethanolamine and phosphatidylglycerol, whereas phospholipase C preferentially degraded phosphatidylethanolamine. During the EDTA treatment, an endogenous phospholipase A1 or a lysophospholipase (or both) was unmasked which caused the formation of free fatty acids in experiments in which no phospholipase was added and which degraded some of the lysophospholipids formed by phospholipase A2. The cells were rapidly killed by the successive Tris-EDTA-phospholipase treatment, but no cell disintegration was observed.