Twenty-one serum samples from 18 wolves (Canis lupus) were collected from 1985 to 1990 from northwestern Montana (USA) and southeastern British Columbia, Canada, and evaluated for antibodies to canine parvovirus (CPV), canine distemper (CD), infectious canine hepatitis, and Lyme disease; we found prevalences of 13 (65%) of 19, five (29%) of 17, seven (36%) of 19, and 0 of 20 wolves for these diseases, respectively. Pups died or disappeared in three of the eight packs studied. In these three packs, adult pack members had CPV titers > or = 1,600 or CD titers > or = 1,250. In packs that successfully raised pups, CPV and CD titers were low. We propose that CPV or CD may have caused some pup mortalities.