Rats were free of Sendai virus, pneumonia virus of mice, coronavirus, Kilham's rat virus, Toolan's H-1 virus, rat parvovirus, rat minute virus, reovirus, Mycoplasma pulmonis, lymphocytic choriomeningitis virus, hantavirus, ciliaassociated respiratory bacillus, Salmonella spp., Shigella spp., Leptospira spp., Spirillum minus, Helicobacter spp. and ectoparasites.