The virion-associated dUTPase activities of caprine arthritis-encephalitis virus (CAEV) and visna virus were determined by using an assay which measure the actual ability of the dUTPase to prevent the dUTP misincorporations into cDNA during reverse transcription. We showed that the CAEV molecular clone from the Cork isolate was dUTPase defective as a result of a single amino acid substitution. Using this point mutant and deletion mutants of CAEV as well as a deletion mutant of visna virus, we demonstrated that dUTPase-deficient viruses replicate similarly to wild-type viruses in dividing cells but show delayed replication in nondividing primary macrophages