Lymphotropic herpesviruses such as Epstein-Barr virus and Herpesvirus saimiri are commonly grouped as gamma-herpesviruses, although overall genome organization and numerous biological properties are quite different in the viruses. To define the relationship more precisely, we sequenced the Kpnl fragments F (6.5 kb) and C (9.8 kb) of the H.saimiri strain No. 11 genome; these DNA fragments were found to contain the genes coding for equivalents of the major DNA binding protein, a putative glycoprotein transport polypeptide, the glycoprotein B, and the DNA polymerase of herpes simplex virus. This DNA segment represents the longest block of contiguous genes with pronounced sequence homologies between herpesviruses of known DNA primary structure. Comparisons confirmed that the two gamma-herpesviruses are related; the group is, however, even more diverse than the alpha-herpesviruses represented by their prototypes, herpes simplex virus and varicella-zoster virus. H. saimiri DNA is strongly depleted in the dinucleotide CpG, possibly the consequence of de novo methylation of persisting viral DNA in lymphoid cells.