The cDNA encoding the catalytic subunit of Drosophila melanogaster (Dm) DNA polymerase delta (Pol delta) was isolated by a combination of PCR amplification and cDNA library screening. The cDNA is 3457 nucleotides in length and contains an open reading frame (ORF) that encodes a protein of 1092 amino acids (124,799 Da). The ORF contains the sequence that was determined for a peptide from the purified catalytic subunit of Dm Pol delta. Polyclonal antibodies raised against Dm Pol delta specifically recognize a protein of the expected size when the cDNA is expressed in either Escherichia coli or insect cells. Comparison of the deduced aa sequence with other Pol delta sequences demonstrates that Pol delta is one of the most highly conserved of the DNA polymerases.