The nucleotide and predicted amino acid sequence of the thymidine kinase (TK) gene of N 569, a bovine encephalitis herpesvirus (BEHV), has been determined and compared with those of avian, bovine and other mammalian herpesvirus TK genes. Striking differences were observed between the nucleotide sequence of this BEHV TK gene and those reported for bovine herpesvirus 1 (BHV-1). A total of 118 base changes, 39 base deletions and 14 base insertions were identified relative to the TK sequence of a BHV-1.2a strain, resulting in a net loss of seven residues. Comparison of the TK sequences of BEHV and the BHV-1 Q 3932 strain with that reported for the BHV-1 6660 strain suggested that the latter may have contained sequencing errors. The most significant difference between the BEHV TK sequence and those of BHV-1 strains was the absence of a contiguous stretch of ten codons.