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In this study, an investigation on whether very low frequency magnetic fields (VLFMF) or induced eddy current cause DNA damage or physiological abnormality in the bacterial cell using lysogenic bacteriophage λ. The bacteriophage λ can multiply by either a lytic or a lysogenic pathway in the E. coli bacterium. When the bacteriophage is growing in the lysogenic state, damage to the cell (e.g. DNA damage by exposure to UV light or mitomycin C) causes the integrated viral DNA (prophage) to exit from the host chromosome and shift to lytic growth, regarded as bacteriophage induction. In this study, the E. coli W3130 lambda_857, which have lambda of lysogenic state (as prophage), was exposed to extremely low frequency (ELF) magnetic fields and the induction of phage was measured by plaque assay. By exposure to 1 mT magnetic fields for about 8 hours, the bacteriophages shifted to lytic growth 1.34 times as often as control. On the other hand, the mitomycin C, mutagenic reagent, showed a shift in bacteriophages from lysogenic to lytic growth 46-times as often as control in this system. These results suggest the following two points: (1) VLF magnetic fields (20 kHz, 1 mT) dose not induce DNA damage strongly in the bacterial cell as mitomycin C action. (2) The induced eddy current rather than VLF magnetic field causes some damage to E. coli cells and the prophages are induced to lytic growth.