Phage lambda infection was investigated for possible production of toxic foreign proteins in Escherichia coli. The target gene transcription was regulated by a T7 promoter, which was initiated under the action of T7 RNA polymerase delivered by infecting phage. Two types of phage infection were investigated. In both cases, deletion of the int gene prevents lysogenic integration. One phage, lambda CE6, contains the Sam7 lysis mutation, so that infectious phage particles remain intracellular. The other phage, lambda CE6M, undergoes the complete lytic pathway so that the infected cell is eventually lysed. The dynamics of phage adsorption, foreign protein synthesis, and cell growth were analyzed as a function of various parameters, such as MOI (multiplicity of infection), cell concentration at infection, culture temperature, and different carbon sources. A low basal level of the foreign protein, beta-galactosidase, was obtained prior to infection, whereas it reached about 0.1 g/L after phage "induction" under appropriate infection conditions. Due to low basal expression, this expression system is useful for the production of toxic foreign proteins.