Pigs are susceptible to M tuberculosis, M bovis, and M avium complex. M avium avium and M avium hominissuis are most frequently isolated; serologic identification of isolates is useful in epidemiologic investigations. Granulomatous lesions are most often found in the cervical, submandibular, and mesenteric lymph nodes, but in advanced disease lesions may also be found in the liver and spleen. Typically, enlarged nodes contain small, white or yellow, caseous foci, usually without any evidence of mineralization. Pigs with disease due to M tuberculosis may have similar regionalized lesions. Pigs are particularly susceptible to M bovis, which is usually acquired from shared grazing or ingestion of contaminated dairy products. This can cause a rapidly progressive, disseminated disease with caseation and liquefaction of lesions. The single intradermal test conducted on the dorsal surface of the ear or in skin of the vulva is often useful for diagnosis. Test responses should be observed at 48 hr after injection of tuberculin.