The Epstein-Barr virus (EBV)-induced intracellular DNA polymerase was assayed in vitro for the ability to utilize the mutagenic nucleotide analog 2-aminopurine deoxyribose triphosphate (d2apTP), incorporating it as the corresponding monophosphate into DNA or poly[d)(A-T)] template. Bacteriophage T4, lymphocyte alpha, and the EBV particle-associated DNA polymerases were assayed simultaneously for direct comparison. Unlike these three polymerases, which were capable of distinguishing between d2apTP and dATP with a strong preference for the latter, the EBV-induced DNA polymerase only weakly distinguished between dATP and d2apTP and incorporated substantial amounts of d2apTP into template. Detergent-treated lymphocyte nuclei undergoing a high level of EBV DNA synthesis were shown to incorporate the 2-aminopurine analog of dATP into viral DNA. The relative inability of the EBV-induced DNA polymerase to distinguish between the two purine nucleotides reported here is consistent with previous reports on the ready incorporation of other nucleotide analogs into DNA polymerases induced by other herpesviruses. Because most antiherpes agents currently in use or under study are nucleotide analogs, the viral mutagenic properties of these drugs should be examined.