In the 1990s, first publications appeared where it was indicated that Mycobacterium avium subsp. paratuberculosis (Map) was more heat resistant than M. bovis and it could survive the HTST pasteurization of milk. Since then, there were many research studies published to confirm the presence of Map in dairy products. It was found that live cells of those micro-organisms were present in samples of marketed pasteurized milk and, also, in cheeses. It is not easy to study the thermal resistance of Map, because the cultivation of Map is an arduous process, and comparing and interpreting the data contained in the reference literature is impeded for reasons attributable to differences among experimental methods applied. The analyses performed with the use of milk heated in tubes, capillary tubes, or in laboratory pasteurizers proved that the pasteurization at a temperature of 63 ºC/30 minutes as well as HTST caused the count of Map cells to decrease by 4 to 7 logarithmic orders. When the experiments were carried out under the conditions of industrial pasteurization, the results obtained were divergent. There are several hypotheses on the thermal resistance of Map in milk, among other things, the formation of clusters of bacteria, physiological adaptation of bacteria that allows them to acquire heat resistance, and physical-chemical changes inside the cells.