Studies will continue to determine basic parameters of the immune response of laboratory cats exposed to virulent and attenuated feline herpesvirus (feline viral rhinotracheitis virus). Cats exposed by intranasal or intramuscular routes will be evaluated for local, cell mediated, and humoral antibody responses. The class of Ig involved in local and humoral responses will be determined using the indirect immunofluorescent test with FITC conjugated monospecific antiserum. The level of immunity in each category (local, CMI, and humoral) will be correlated with protection against virulent virus exposure.