Homogeneous DNA polymerase ("reverse transcriptase") from avian myeoblastosis virus was assayed for exodeoxyribonuclease activity. The substrates were defined template-initiator complexes in which different radioactive nucleotides were present at the 3'-OH termini of the initiator. Even when the number of molecules of enzyme was equal to the number of initiator termini there was no significant release of radioactivity with any of the template-initiator combinations tested. Under similar conditions, the nuclease activity associated with either Escherichia coli or T4DNA polymerases rendered more than 90% of the initiator termini acid-soluble. The ratio of exodeoxyribonuclease activity to protein with avian myeoblastosis DNA polymerase is less than 0.003% of that obtained with E. coli DNA polymerase I. Furthermore, avian myeloblastosis virus DNA polymerase failed to excise mispaired terminal nucleotides in both the presence and absence of polymerization.