Computer-matching of amino acid sequences predicted from the complete EBV DNA sequence against the known HSV gene sequences has revealed significant homology between two EBV reading frames and the HSV1 and ESV2 140K and 38K proteins which are associated with ribonudeotide reductase activity. The two genes are arranged tandemly as in HSV though it appears that, unlike HSV, the two mRNAs are not 3′ co-terminal. We have mapped two promoters predicted from the DNA sequence for these genes and shown them to be transcribed at a similar stage in the virus life cycle to that of the HSV genes.