[en] Near ultraviolet light (UV) causes lethal and mutagenic effects in Escherichia coli sensitized with 8-methoxypsoralen (8-MOP). A strain of B family, Hs30R uvrA^-, is 5-times more sensitive to the treatment than H/r30R. Frequency of the induced mutation of the both strains was measured with respect to the phenotypic reversion of arginine auxotrophy. The frequency of Hs30R is 20-times higher than that of H/r30R. Massive induction of prophage lambda was observed when lysogenic bacteria, AB1157 (lambda), were exposed to near UV in the presence of 8-MOP. The induced mutation and the prophage induction support the concept that major damage responsible for killing of the cells by psoralens plus near UV is in DNA. (auth.)