Previously it has been shown that a DISC gHdeleted HSV-1 can protect against HSV-1 challenge in the mouse ear model (Farrell et al., 1994) . The DISC virus, by virtue of its capacity for a single round of replication in normal cells, is more potent than a non-replicating, inactivated virus preparation. A gHdeleted HSV-2 virus has also been tested as a vaccine in a guinea pig model. Animals vaccinated with DISC HSV-2 showed complete protection against primary HSV-2 induced disease, even when challenged six months after vaccination (Boursnell et al., 1997) . The animals were also almost completely protected against recurrent disease.