Exposure of a herpes simplex virus type 1 to UV light resulted in a multi-component survival curve. Plaques formed by the UV-irradiated virus were smaller than those induced by untreated virus. Maximum plaque counts in cultures inoculated with non-irradiated virus were obtained on the 4th day; when using irradiated virus, the plaque count continued to increase during the subsequent 4 days. These findings may reflect host cell repair. A non-linear relationship between plaque count and virus dilution, indicative of multiplicity reactivation, was observed in cultures infected with heavily irradiated virus.