Bovine herpesvirus 1 isolates contain variable copy numbers of GC-rich tandem repeats in the gI non-coding regions of their genomes. 
A polymerase chain reaction (PCR) targeted to the central portion of the bovine herpesvirus 1 (BHV1) genome, and overlapping the 3' untranslated end of the gI glycoprotein, was used to amplify BHV1 genomic sequences.  PCR products generated from cell cultures infected with BHV1.1 were consistently smaller than the corresponding products from cells infected with BHV1.2.  The nature of the sequence differences between these isolates within the target region was found to be a consequence of variable numbers of small GC rich repeats, particularly the sequence 5'-G(A/T)CC-3', present in the region downstream of the gI coding region.  Based on these differences a modified PCR protocol which readily discriminated between several BHV1.1 and BHV1.2 strains was devised.