A number of diseases affecting the CNS occur in the dog and can be used as models for gene therapy in a large brain. HSV-1 has several potential advantages as a vector to transfer genes into the CNS. However, the ability of HSV-1 to infect CNS cells varies among species and no information was available for the dog. When the nonpathogenic 1716 strain of HSV-1 was injected into the brains of normal dogs it established a latent infection without signs of pathology. Thus, it appears to be suitable as a vector for therapeutic, or marker genes, in this species.