and J. S. Reif. Studies of canine respiratory viruses. I. Experimental infection of dogs with an SV5-like canine parainfluenza agent. Amer J Epidem 94: 147-165, 1971.-A parainfluenza virus which was recovered from a case of kennel cough at the University of Pennsylvania kennels was found capable of infecting all dogs without pre-existing antibodies on introduction into the nasopharynx, as proven by virus recovery, for 5 to 9 days after inoculation and by rises in specific antibodies. The infection was readily transmitted to primary and secondary contacts, providing exposure was initiated during the virus shedding period. Dogs found to have had serum neutralizing antibody previous to experimental exposure to the virus did not become infected. Similarly, dogs with antibodies induced by experimental infection were resistant to re-infection when challenged by nasopharyngeal inoculation 70 days after their first exposure. About 60% of the dogs infected by either inoculation or contact developed clinical signs of tracheobronchitis. The characteristic sign consisted of spontaneous cough which lasted for 2 to 12 plus days. Evidence of pulmonary disease was confirmed by radiologic and post-mortem examination. Histopathologic lesions included interstitial pneumonia, bronchopneumonia, bronchitis and bronchiolitis. Treatment with cortisone did not influence the susceptibility of the animals to the virus or enhance the severity of the disease. Although the neutralizing (HAD-N) and hemagglutination-inhibition (HI) antibodies occasionally appeared in the early part of the second week, peak HI titers were reached between 14 and 21 days while maximal HAD-N levels occurred at about 30 days. About 3J^ months after infection, titers ranging from 1:32 to 1:128 were still detectable when assayed by either test. Seventeen of 60 (28%) dogs admitted to the clinic for any reason were found to have significant-levels of HAD-N antibody to the virus. The virus was found to be antigenically related but distinguishable from the simian virus, SV5. antibodies; dog diseases; infection, experimental; kennel cough; parainfluenza viruses; respiratory tract diseases; tracheobronchitis, canine In searches aimed at establishing the cough," a number of viral agents have been etiology of canine tracheobronchitis or la-implicated, ryngotracheitis, also known as "kennel Ditchfield et al.