Mismatch repair (MMR) systems are evolutionarily conserved and play a primary role in mutation avoidance by removing base-base and small insertion-deletion mismatches that arise during DNA replication (31). In addition, MMR factors are required for the repair of mismatches in heteroduplex DNA (hDNA) that form as a result of sequence heterologies between recombining sequences (6, 41, 43). MMR also acts to inhibit recombination between moderately divergent (homeologous) sequences (11, 42). The roles of MMR during recombination are believed to reffect the interaction of MMR factors with mismatches that arise in hDNA or possibly with other structures such as Holliday junctions (2, 33). The full range of effects that MMR can exert on mitotic and meiotic recombination have been discussed elsewhere (11) and will only be summarized brieffy here. The purpose of this review is to highlight recent results that have furthered our understanding of interactions between MMR factors and mitotic recombination intermediates.