Eukaryotic DNA polymerase beta (pol beta) can catalyze DNA synthesis during base excision DNA repair. It is shown here that pol beta also catalyzes release of 5'-terminal deoxyribose phosphate (dRP) residues from incised apurinic-apyrimidinic sites, which are common intermediate products in base excision repair. The catalytic domain for this activity resides within an amino-terminal 8-kilodalton fragment of pol beta, which comprises a distinct structural domain of the enzyme. Magnesium is required for the release of dRP from double-stranded DNA but not from a single-stranded oligonucleotide. Analysis of the released products indicates that the excision reaction occurs by beta-elimination rather than hydrolysis.