Morphologic changes in rabbit cornea accompanying herpes simplex keratitis especially under the treatment of ethyldeoxyuridine (EDU) are summarized in regard to clinical aspects, light microscopy and electron microscopy. Untreated eyes show virus-dependent characteristic changes of the cell structure: peripheral migration of the cell chromatin, swelling of the nucleus, and disappearance of the nucleolus are persistent. In the nucleus as well as in the cytoplasm mature and immature virus particles are visible which demonstrate the normal virus-replication course. In the EDU treated cornea these particular changes are observed only in the primary stage. After prolonged treatment in the nucleus of the infected cells there are only immature virus particles with optically empty center. This can be evaluated as a sign of inhibition of the normal replication. No virus formation was detected in the cytoplasm. After 7 day treatment of EDU, the corneal epithelium is almost of normal structural appearance. Accordingly, the present results on the rabbit seem to correlate well with the reported therapeutic antiherpetic studies in the human cornea.