A novel phage double-lysogen was developed to produce an intracellular protein and disrupt the host cell in the same reactor. Using this double-lysogen, we could simplify the recovering processes without cell harvest and disruption. Construction of the double-lysogen is based on the fact that a lysogen of a phage can be superinfected by another phage with different immunity. The single-lysogen of Escherichia coli, P90c/λHL1, was superinfected with bacteriophage Φ434 to produce a double-lysogen, in which phage genomes from each phage coexisted in the host chromosome. Two different inducers were used to induce the double-lysogen to produce a protein and to lyse the host cell. The first phage genome, λHL1, the prophage of the original lysogen, containing the temperature sensitive cI₈₅₇, lacZ and defective Q genes was induced by increasing temperature to produce β-galactosidase, an intracellular reporter protein. The overproduction of β-galactosidase was carried out without experiencing the cell lysis due to the defective Q gene. After the temperature shift, the second prophage from the lysogen MS21/Φ434 was induced by mitomycin C or ultra-violet light to lyse the cell. The lysis of the cell releases the intracellular protein to the outer space. The cell lysis was confirmed by the decrease of cell density and the increase of the extracellular activity of β-galactosidase at the same time.