The nucleotide sequence of the gB glycoprotein gene of HSV-2 has been determined and compared with the homologous gene of HSV-1. The two genes are specified by the same total number of codons (904); eight additional codons of the HSV-1 gene are found within the signal sequence, and eight additional codons of the HSV-2 gene are found at three different sites in the gene. The signal cleavage, membrane-spanning, and eight potential N-linked oligosaccharide sites, as well as 5'- and 3'-regulatory signals are largely conserved. The overall amino acid homology is 85%; least conserved are the N- and C-terminal regions of the protein. Secondary structure plots were determined for the two proteins, and the structures were compared with each other and with alterations in structure due to several mutations in the HSV-1 gB gene for which sequence analysis is available. The high homology in primary and secondary structure suggests a conserved, essential function for the gene.