Elevated and sustained cell replication, together with a decrease in apoptosis, is considered to be the main mechanism of hepatic tumor promotion due to peroxisome proliferators. In contrast, the role of oxidative stress and DNA damage in the carcinogenic mechanism is less well understood. In view of possible induction of DNA damage by peroxisome proliferators, DNA repair mechanisms may be an important factor to consider in the mechanism of action of these compounds. Here, the ability of peroxisome proliferators to induce expression of base excision repair enzymes was examined. WY-14,643, a potent carcinogen, increased expression of several base excision DNA repair enzymes in a dose- and time-dependent manner. Importantly, expression of enzymes that do not repair oxidative DNA damage was not changed. Moreover, less potent members of the peroxisome proliferator group had much weaker or no effects on expression of DNA repair enzymes when compared with WY-14,643. Collectively, these data suggest that DNA base excision repair may be an important factor in peroxisome proliferator-induced carcinogenesis and that induction of DNA repair might provide further evidence supporting a role of oxidative DNA damage by peroxisome proliferators.