Six 3 to 4 weeks old, cesarian-derived lambs were inoculated with ovine an adenovirus isolate 475N. Inoculated lambs showed moderate clinical signs of respiratory distress, conjunctivitis, and loose feces during the 10-day observation period. Virus was detected from nasal and conjunctival swabs starting on postinoculation day (PID) 2. Virus was detected in the feces in a inconsistent fashion. At necropsy, virus was present in the lung, tonsils, and bronchial and mediastinal lymph nodes of lambs necropsied on PID 5 and 7. Tissue samples from gastrointestinal tract and kidney were negative for the virus. Presence of virus in the feces was believed to be from replication in tonsillar tissue. At necropsy, lambs showed signs of pneumonia and numerous intranuclear inclusion bodies were detected in affected lung tissue. Virus neutralizing antibodies appeared at low levels in serum on PID 6 and reached higher levels by PID 10. Six ovine adenovirus prototype species, three uncharacterized ovine and bovine adenoviruses isolates and two uncharacterized llama adenoviruses isolates were digested with four different restriction enzymes. Digested viral DNA was separated in 0.7% agarose gels. The enzymes Barn HI, Eco RI, Hind III, and Pst I digested viral DNA and produced 2-10 bands. The profile of the band distribution permitted the differentiation of the viruses under study. However, further studies using multiple isolates of each species are required to determine if this procedure will efficiently distinguish different species of ruminant adenoviruses. Ten adenoviruses from sheep (including the six prototype species), one from bovine and one from llama were studied by virus neutralization test to determine their degree of antigenic similarities. Reciprocal virus neutralization tests were performed and the degree of antigenic similarities, i.e., strain differentiation was determined by criteria established by the International Committee for the Nomenclature of Viruses. Isolates 32CN (a bovine adenovirus) and 475N (an ovine adenovirus) were antigenically identical and not neutralized by any of the prototype species antiserum. They are candidates for a new species of ruminant adenoviruses. Ovine adenovirus isolate 47F was shown to be a member of OAV-5 species while the llama adenovirus strain represents a newly recognized species for this animal. / Graduation date: 1996