The influence of infectious dose and nutrition on the pig susceptibility to Mycobacterium intracellulare, serotype 4, 8, was studied with 48 pigs--crossbreds LW X X L--divided into four equal groups. All groups of pigs were fed ad libitum by the mixture consisting of maize, wheat, barley, soybean meal, salt lick and MKP 1 mineral feed supplement. Individual groups were given different levels of meals of animal origin and biofactor supplements containing vitamins A, D2, B2, B12 and niacin. Single per os administration of the infectious dose of Mycobacterium intracellulare amounted to 0.01 or 0.1 mg of mycobacterial culture per one kg of live weight. The extent of patho-anatomical findings depended on the infection intensity. The infectious dose of 0.01 mg of the culture resulted in the changes in the form of exudative lymphadenitis with characteristic caseous degeneration in lymphatic glands only in three out of 24 pigs, i. e. in 12.5%. A tenfold dose of mycobacteria caused caseous lesions in the mandibular and intestinal glands in 50% out of 22 infected animals. The result of complex examination of the lymph glands proves the favourable effect of biofactor supplement on the resistance in pigs, particularly those infected with lower mycobacterial doses. Mycobacteriosis was proved in all experimental pigs fed the mixture containing no biofactor supplement. In the group of animals fed the mixture with biofactor supplement the result was positive in 66.6% of infected animals. It was observed that the biofactor supplement also had a positive influence on active excretion of M. intracellulare by faeces. In pigs infected with high dose of mycobacteria this excretion was proved in 27.2% of animals. In the pigs fed the mixture containing biofactor supplement, regardless of the infectious dose and amount of animal proteins, no elimination of mycobacteria by faeces was observed. Out of 14 pigs with the microscopic finding of tuberculosis in the lymph glands, the reaction with an induration diameter larger than 10 mm was found in eight animals, i. e. 57.2%, after intradermal tuberculinization with purified avian tuberculin after 74 days from infection.