In the long unique region of the genome of herpes simplex virus type 1 (HSV-1), the genes for DNA polymerase and the major DNA binding protein are arranged in a head to head manner, with an origin of DNA replication (termed OriL) located between them. This paper reports an 8400 base pair DNA sequence containing both genes and the origin, obtained mostly by M13/dideoxy analysis of plasmid cloned fragments. Amino acid sequences of the two proteins were deduced. Homologues of both genes were detected in the genome sequence of the distantly related Epstein-Barr virus (EBV). Arrangement of these HSV-1 and EBV genes differs in genome location and in relative orientation. A part of HSV-1 DNA polymerase was found to be similar to a sequence in adenovirus 2 DNA polymerase, but the significance of this is unclear. Since a DNA sequence in the locality of OriL deletes on plasmid cloning, this region was analysed using virus DNA. A palindrome with 72-residue arms was found, which shows great similarity to the better characterized origin, OriS.