The genomes of 10 equine herpcsvirus 1 (EHV-I) strains isolated in Argentina from 1979 to 1991, and a Japanese HH1 reference strain were compared by restriction endonuclease analysis. Two restriction enzymes, BamHI and Bg/II, were used and analysis of the electropherotypes did not show significant differences among isolates obtained from horses with different clinical signs. This suggests that the EHV-1 isolates studied, which circulated in Argentina for more than 10 years, belong to a single genotype.