The effect of experimental primary-stage feline immunodeficiency virus (FIV) infection on feline calicivirus (FCV) vaccination and challenge in cats was studied. Clinical signs of acute FCV disease were more widespread in the cats which were infected with FIV than in those which were not. FIV infection also prolonged shedding of FCV, with more of the FIV-infected cats becoming chronic carriers. Although vaccination induced protection against acute FCV disease, this was to a lesser degree in FIV-infected cats. Vaccination by itself also appeared to enhance long-term virus shedding. There was evidence of an impaired anamnestic FCV-neutralizing antibody response in FIV-infected cats following FCV challenge.