Autolysis of Escherichia coli induced by a shock treatment with 10−3M EDTA, pH 6.5 was investigated. Mutants presenting reduced rates of EDTA-induced autolysis were isolated. A remarkable feature of these mutants was their tolerance to penicillin G, cephaloridine and moenomycin. Furthermore, a reduced level of peptidoglycan endopeptidase or N-acetylmuramidase activity was observed. Penicillin-binding protein patterns were unaltered.