Experimental tuberculosis in mice infected with cultures of the H(37)Rv strain exhibiting high degrees of resistance to SM, PAS and INH and subsequently treated with single administration of KM, CS and TH respectively was carried out, Also a clinical observation of reversal of infectiousness of the tubercle bacilli of the sputum of patients with chronic pulmonary tuberculosis by this treatment regime was performed. Kanamycin treatment of 1mg per mouce scarcely showed the effectiveness to all of the resistant strains. Cycloserine treatment of 2.5mg per mouce did not show any improvement of the tuberculous lesions. It is assumed that many inactive factors to CS in mouse body take part in this uneffectiveness of CS, but especially the activity of D-alanine does, While, ethionamide treatment of 1mg per mouce revealed marked effectiveness to each resistant strain and it is noted that TH treatment of 1mg per mouce was as effective as INH treatment of 0.1mg per mouce. In the clinical observation, single administration of KM, CS or TH revealed no remarkable effectiveness to the patients with triple resistant tubercle bacilli to SM, PAS anp INH. Especially this treatment regime to the patients with chronic far advanced, active pulmonary tuberculosis scarcely brought reversal of infectiousness. It may be concluded that the single administration of TH should not be done because of easy appearence of the resistance in short time.