Numbers of unvaccinated Mexican wolves (Canis lupus baileyi) born in the Mexican Wolf Experimental Population Area in Arizona and New Mexico with positive titers for canine distemper virus (CDV) and canine parvovirus (CPV). Only wolves younger than 2 yr old when sampled are included. No samples were collected in 2004. Before July 2012, antibodies to CDV were detected via serum virus neutralization or immunofluorescent antibody detection. After July 2012, an enzyme-linked immunosorbent assay was used for the CDV test. Antibodies to CPV were detected via hemagglutination inhibition in all years.