Recombinational repair of double-strand breaks (DSBs), traditionally believed to be an error-free DNA repair pathway, was recently shown to increase the frequency of mutations in a nearby interval. The reversion rate of trp1 alleles (either nonsense or frameshift mutations) near an HO-endonuclease cleavage site is increased at least 100-fold among cells that have experienced an HO-mediated DSB. We report here that in strains deleted for rev3 this DSB-associated reversion of a nonsense mutation was greatly decreased. Thus REV3, which encodes a subunit of the translesion DNA polymerase zeta, was responsible for the majority of these base substitution errors near a DSB. However, rev3 strains showed no decrease in HO-stimulated recombination, implying that another DNA polymerase also functioned in recombinational repair of a DSB. Reversion of trp1 frameshift alleles near a DSB was not reduced in rev3 strains, indicating that another polymerase could act during DSB repair to make these frameshift errors. Analysis of spontaneous reversion in haploid strains suggested that Rev3p had a greater role in making point mutations than in frameshift mutations.