Herpesviruses and poxviruses are known to encode the DNA repair enzyme uracil-DNA glycosylase (UNG), an enzyme involved in the base excision repair pathway that specifically removes the RNA base uracil from DNA, while at least one retrovirus (human immunodeficiency virus type 1) packages cellular UNG into virus particles. In these instances, UNG is implicated as being important in virus replication. However, a clear understanding of the role(s) of UNG in virus replication remains elusive. Herpesviruses, poxviruses and some retroviruses encode dUTPase, an enzyme that can minimize the misincorporation of uracil into DNA. The encoding of dUTPase by these viruses also implies their importance in virus replication. An understanding at the molecular level of how these viruses replicate in non-dividing cells should provide clues to the biological relevance of UNG and dUTPase function in virus replication.