During the hunting seasons 1995-96 to 1997-98, 19 red deer from the Upper Susa Valley (Cottian Alps) were examined for paratuberculosis (Johne's disease). Specific DNA amplification on mesenteric lymph nodes detected Mycobacterium avium paratuberculosis in 17 animals. Ten of these red deer were tested for serum antibodies by the AGID and ELISA tests, nine being negative. Three isolates from infected deer were genetically characterized by an arbitrarily primed polymerase chain reaction, and showed similar genetic polymorphism to that of bovine strains isolated in different Italian areas. The study showed that paratuberculosis is present in red deer of the Upper Susa Valley and that serological tests are not an efficient means for monitoring this infection.