Sterile drinking water samples were artificially colonized with M. Kansasii, M. gordonae and M. fortuitum suspensions (the numbers of viable unite in 1 ml were 1.2 x 10(3), 48.5 and 3.2 x 10(3), respectively) prepared from mycobacterial strains replicated in Tween 80-free liquid Dubos medium STO. The contaminated water samples were irradiated from a rotary cobalt-60 source (gamma radiation, E = 1.17 and 1.33 MeV, dose intensity 1 kJ/kg.h at room temperature) with doses 0.7, 1.5, 2.2, 3, 9, 16 and 27 kJ/kg. The disinfecting effectiveness was assessed by direct cultivation tests (0.5 ml volumes of water inoculated on egg medium) and by cultivation on membrane filters after filtrating the whole amount of the water examined (about 500 ml). Fully positive disinfecting effects were recorded in M. kansasii and M fortuitum irradiated with 9 kJ/kg and in M. gordonae after irradiation with 1.5 kJ/kg. The calculated value of D10 = 0.4 kJ/kg (i.e. the dose radiation that reduces the number if viable mycobacteria by an order of magnitude) is suggestive of a strong disinfecting effect of ionizing radiation on the tested strains of potentially pathogenic mycobacteria. The results indicate that the use of ionizing radiation to disinfect mycobacteria that are difficult to remove with other methods which, as a rule, cannot ensure the permanent disinfection.