An analysis of genetic variability of herpes simplex virus type 1 and
type 2 populations of the Madrid (Spain) area has been carried out by
digestion of viral DNA with restriction endonucleases. The index of nu
cleotide diversity indicated that herpes simplex virus type 1 has a sl
ightly, although statistically significant, higher degree of heterogen
eity than type 2. A phylogenetic tree for each type of virus has been
constructed. The evolutionary pattern followed by both types of viruse
s ('star-like' topology) suggest that all the isolates analyzed evolve
d from a unique origin for each type of virus.