A case of avian tuberculosis in a horse, with fatal course, is reported. The animal was imported from Poland and became ill after some weeks, in the beginning showing non-specific symptoms which became more severe until death supervened. Post-mortem examination showed a generalised form of tuberculosis. The most important lesions were seen in the lungs, liver, kidneys, spleen, intestinal tract, bones, bone marrow, and the internal lymph nodes. Beside chronic proliferative tuberculosis of the organs, many exudative foci were found with remarkably abundant acid fast bacilli. Mixed lesions were seen, too. Mycobacterium avium was isolated in microbiological examination. The pathogenesis of the infection, the predisposing factors leading to this generalised and open form of tuberculosis and the increasing importance of avian tuberculosis for animals and man are discussed.