The nucleotide sequence of part of the capsid-coding region of the genome is determined. This sequence is then compared with a computerised database of the same genomic region of other strains of FMD virus. A dendrogram, analogous to a family tree, can then be constructed showing the relationships between viruses. The percentage difference in nucleotide sequence of any pair of viruses is derived by reading the value off the x axis of the first point where the branches from each meet.