The metabolism of phospholipids of Escherichia coli was studied under conditions which inhibit various metabolic processes. Phospholipid synthesis and turnover were not inhibited by growth-inhibitory amounts of various antibiotics. Turnover of phosphatidylglycerol (PG) was inhibited by small amounts of dinitrophenol and by anaerobiosis. Turnover of phosphatidylethanolamine (PE), which is not detected in control cultures, was demonstrated under conditions of incipient lysis. When cells were shifted down from a rich to a poor medium, PE synthesis was inhibited, and incorporation of glycerol into the distal position of PG was stimulated. Under these conditions, turnover of the phosphate and the acylated glycerol moieties of PG was inhibited. Increased synthesis of PE was detected when filamentous cells were induced to make septa. The results indicate that PE synthesis is related to growth and cell division, whereas PG metabolism is related to other cell processes.