Out of 207 cases of pulmonary resection, the author studied tubercle bacilli in 314 foci by smear, culture and estimation of resistance with the purpose to find out the characteristic traits of these bacilli, and obtained the following results. Smear positive ones occupy 94.2 per cent while culture positive only 45.2 per cent, and smear positive, culture negative ones occupy 49.7 per cent. The smear positive rate by various methods of staining is poorest in the case of Ziehl-Neelsen method and highest in the fluorescent method. There can be found no difference in the culture result whether cultured in an untreated 1% ogawa medim, 4% sodinm hydrocide-treated medium or untreated-3% ogawa medium. It seems that the question whether or not the tubercle bacilli in the focus are culture positive does not depend so much on the kind of chemotherapy, the dose of drug administered or duration of the treatment, but it rather depends on the character of the focus, and the effect of the chemotherapy affects indirectly ans secondarily, and that after the closing of focus and the hardening of contents with lapse of time smear positive-culture negative cases will increase in number. In the case given chemotherapy and collapse treatment prior to the resection, no fixed relationship can be observed in the cavity but in the case of the caseous cavity accompanied by penumothorax many culture positive ones can be recognized. In the case whose bacillib in the focus proved to be culture negative the majority of them show the normal value of the blood sedimentation before operation, and in these showing the value over 21 mm most of the bacilli in the cavity prove to be culture positive. The acquiring of resistance by the bacilli in the focus is dependent on the character of the focus rather than the dose of drugs or the duration of the treatment. In the open focus treated with a large dose of drug for a long period of time the resistance of bacilli in the focus is high, while the resistance of the bacilli in the encapsulated focus is generally low. However, even in the same kind of foci the resistance of bacilli tends to be higher in the foci whose contents are softer, and the same thing can be said of bacilli in different kinds of foci. Even in the cavity which stopped expelling bacilli soon after the start of chemotherapy, when the chmotherapy is continued for a long time afterward, generally there is no rising tendency in the resistance of bacilli in the focus. As for the degree of resistance acquired by bacilli against various drugs, the majority acquire a higher resistance against SM, and the resistance against PAS is on the whole low, while that ahainst INAH is approxiamtely similar to that against SM.