Serum samples were collected from 29 Rocky Mountain bighorn sheep (Ovis canadensis) in their natural habitats in Colorado and Wyoming. Sera were tested for the presence of antibodies to six viruses. Hemagglutination inhibition tests indicated 18 sheep had antibodies to PI3, with 9 having titers greater than 1:8 and 24 sheep had antibodies to bovine parvovirus 1, with 24 having titers greater than 1:8. Serum neutralization tests showed one sheep had antibodies to the viruses of blue-tongue and bovine viral diarrhea while no animals had titers to infectious bovine rhinotracheitis. Complement fixation tests revealed 13 sheep had antibodies to the group specific CF antigen of the adenoviruses. Only one animal possessed the group specific precipitating antibody.