Similar open reading frames (ORF) overlapping the thymidine kinase (TK) gene on the opposite strand or being close to it have been identified in 8 herpesviruses (Jacobson et al., 1989). Study of the DNA sequence of BHV-1 TK gene published by Mittal and Field (1989) and Kit and Kit (1986) revealed the existence of a similar ORF in this virus genome, too.