1) Marked tuberculous changes were observed in the lungs of rabbits inoculated with the human tubercle bacilli (Nakano strain) of 1/1000 mg, 1/100 mg or 10 mg, even in the 16th week after inoculation. 2) In the lungs of the animals treated with SM or INAH during the first 8 weeks, less tuberculous changes were observed than in these of the controls, at the end of 16th week after the bacilli inoculation. The effectiveness of INAH would be somewhat pronounced as compared with that of SM