Eight reference strains of the nine accepted bovine adenovirus serotypes were compared by means of restriction enzyme (RE) analysis of the viral DNA. The study was carried out with the aim to identify RE giving restriction patterns which are particularly feasible for identification of new isolates and useful for their classification into subgroups. The BamHI, EcoRI, HindIII and PstI enzymes were feasible for identification of strains. The classification of bovine adenovirus (BAV) into subgroup 1 (BAV-1, 2, 3 and 9) and subgroup 2 (BAV-4, 5, 6, 7 and 8) was supported by (i) the significant difference in genome size between members of subgroup 1 (ranging from 32.73 to 37.67 kb) and members of subgroup 2 (ranging from 28.78 to 31.18 kb); and (ii) the observation that the nucleotide sequence recognized by EcoRI is less frequent in the genomes of subgroup 1 members - yielding 4-7 RE fragments - than in the genomes of subgroup 2 members - yielding 10-16 RE fragments.