The recF, recO, and recR genes were originally identified as those affecting the RecF pathway of recombination in Escherichia coli cells. Several lines of evidence suggest that the recF, recO, and recR genes function at the same step of recombination and postreplication repair. In this work, we report that null mutations in recF, recO, or recR greatly reduce UV-radiation mutagenesis (UVM) in an assay for reversion from a Trp− (trpE65) to a Trp+ phenotypes. Introduction of the defective lexA51 mutation [lexA51(Def)] and/or UmuD′ into recF, recO, and recR mutants failed to restore normal UVM in the mutants. On the other hand, the presence of recA2020, a suppressor mutation for recF, recO, and recR mutations, restored normal UVM in recF, recO, and recR mutants. These results indicate an involvement of the recF, recO, and recR genes and their products in UVM, possibly by affecting the third role of RecA in UVM.