DNA polymerase-alpha and -beta were fractionated from the chromatin of regenerating liver of young and old mice. The DNA polymerases were resolved from each other and partially purified by DEAE-cellulose, phosphocellulose, and DNA-cellulose column chromatography. No significant age-related difference in the kinetics of heat inactivation was observed for either DNA polymerase. No age-dependent difference was found in the fidelity with which these enzymes copied phi X174 DNA. These results suggest that the functional properties of these DNA polymerases do not change with age as is postulated in some theories of aging.