We have sequenced a gene in human cytomegalovirus and a homologous gene in human herpesvirus 6 which could specify a product related to protein kinases. This gene appears to be generic in the herpesvirus family as homologues were found in three other human herpesviruses. The five sequences were aligned and found to be quite divergent. Some of the differences occur at amino acid positions which are functionally important and highly conserved in known protein kinases. Hence these genes may represent a significant departure from known protein kinases in terms of structure and/or function.