Herpes simplex virus (HSV) produces a wide variety of ocular disease in man. Although host factors are important in determining this variation, it is possible that the different clinical patterns of herpetic ocular disease may be attributed at least partially to the differing biological behavior of specific strains of HSV. To test this theory, we compared the anterior segment disease produced by infecting rabbit corneas with seven different strains of HSV. We found that these seven different strains produced different patterns of ocular disease in the rabbit eye. This also may occur in humans, and we hope to define the biological differences that cause one strain to produce disease more severe than that produced by another strain.