We present an analysis of 43,658 bp of contiguous nucleotide sequence comprising the right terminal region (conventional orientation) of the unique protein-coding component (L-DNA) of the herpesvirus saimiri (HVS) genome. Within this region lie the genes encoding the 160-kDa virion protein, which is homologous to the 140-kDa membrane antigen of Epstein-Barr virus (EBV), thymidylate synthase (TS), and the immediate-early (IE) 52-kDa protein which is homologous to the EBV BMLF1 product. The 160-kDa gene of HVS lies at the right terminus of HVS L-DNA, its homologue in EBV occurring at the left terminus of the EBV genome (conventional orientation). The TS gene of HVS occurs within a group of 5 genes that have no homologues in EBV. The translation product of one of these genes, ECRF3, shows amino acid sequence and hydrophobicity pattern similarities to the HCMV and cellular G-protein-coupled receptor family of proteins. Another, ECLF2, is homologous to the cyclin family of cellular proteins. The 5 nonconserved genes lie adjacent to the 160-kDa gene. In EBV, the region to the right of the 140-kDa gene (BNRF1) contains the latent replication origin (OriP) and the open reading frames BCRF1, BWRF1 (repeated 12 times), BYRF1, BHLF1, and BHRF1, counterparts of which are not present in this position in HVS. The subsequent 18 genes in EBV (BFLF2 to BLRF2, approximate positions 56,000-89,500) are represented in HVS, and the relative positions and orientations of these genes are directly comparable between the two viruses. There then occurs a nonhomologous gene in HVS, and genes BLLF2 to BZLF1 (positions 89,500 to 103,200) in EBV which are not present in this region of HVS, before collinearity resumes. Thus, the HVS sequence presented here shows general collinearity between conserved genes in the right terminal region of HVS and the left terminal region of EBV and reveals the presence of two sets of unique genes which occur in exactly analogous positions in HVS and EBV.