The members of Mycobacterium avium complex belong to the most common agents causing mycobacterioses in humans. They are classified as a potentially patogenic mycobacteria, although Mycobacterium avium subsp. avium represent veterinary and economic risks in birds (mainly poultry) as well as mammals (pigs etc.). Infected animals and their products (mainly eggs) often come from small household production and pose a risk for human health. The second member of this complex, Mycobacterium avium subsp. hominissuis, is commonly isolated from humans and pigs. For both hosts, the sources are particularly various components of the environment (peat, compost and surface water). The third member, Mycobacterium intracellulare is commonly found in soil and water which was not treated with chlorine. (Nowadays, ozone is used for the treatment of potable water). Consequently, infections of humans and animals caused by this agent are expected to rise.