Within the framework of the electron-topological approach the structure-antitubercular activity relationship was investigated in a series of thiosemicarbazone derivatives. The series in view included 71 compounds. For each compound conformational and quantum-chemical calculations were carried out. An activity feature gave a satisfactory description of the class of active compounds: two parameters, alpha(a) and P-a, estimating the probabilities of its realization had the values equal to 0.935 and 0.914, correspondingly. At the same time the feature of inactivity found (''the break of activity'') was realized within the class of inactive compounds with the probabilities alpha(b) = 0.749 and P-b = 0.950. Eight compounds not included in the teaching sample were tested for features presence. The results of the test demonstrated a high ability of the electron-topological method to predict the activity needed.