Lysis of Escherichia coli by bacteriophage phi X174 is caused by the phage protein E. As protein E is devoid of enzymatic activities it has been postulated that lysis is the result of an induction of the autolytic enzymes of the host. This hypothesis was investigated by comparing the murein composition before and during lysis of either phi X174 infected cells or protein E induced lysis of E. coli. Additionally, protein E-mediated lysis was compared with induction of the autolytic system by EDTA. The analysis showed that the overall composition of murein is not changed after induction of protein E-mediated lysis. Nevertheless, murein degradation seems to be stimulated by the action of protein E as shown by an increase in the total amount of murein turnover products by about 10%. It could be shown that an intact murein sacculus prevents the phages from being released.