For development of an autolytic Escherichia coil protein expression system, T4 bacteriophage (T4)-mediated E. coli disruption was investigated. At least two types of E. coli cell lysis, "lysis from without" (LO) and "lysis from within" (LI), are known to be induced by T4. The efficiency of cell disruption was monitored by the release of beta-galactosidase from the cells. In the case of multiplicity of infection (m.o.i.) of 100, the infected cells mere lysed without proliferation of the progeny phage (LO). When the cells were infected at a m.o.i. of 5, slow cell lysis (LI) was observed. The beta-galactosidase activity detected in the supernatant of the culture subjected to LO was the same as that in the lysate produced by chloroform treatment or sonication of the T4-uninfected culture, but about twice that in the supernatant of the culture subjected to LI. At a m.o.i. of 0.01, delayed onset of cell lysis, called lysis inhibition (LIN), was observed. However, the cells In LIN state were simultaneously lysed upon shifting of the temperature from 37 degrees C to 0 degrees C, which was accompanied by an increase in extracellular beta-galactosidase activity.