The intraoperative cytological quick-examinations and quick-tests may influence way and type of the operation in cases of uncertain nature. They may lead to the fact that the original schedule of operation is kept to or changed. Thus, the operation is performed according to the situation, and lung tissue may be saved. Therefore, the possibility of a rapid diagnosis during the operation is of great importance. It is, however, often difficult or risky due to a potential tumour transplantation or due to other complications, to obtain respective tissue material for histological examination, above all, in such cases where the foci are located very deeply in the lung parenchyma. Therefore, the authors deal with the cytological examinations of 216 tissue samples taken from 187 patients intraoperatively (obtained by thoracotomy: 119 cases, by mediastinoscopy: 57 cases, by various surgical interventions: 20 cases). In 155 cases (82 per cent) the findings proved to be rightly positive or negative with regard to their malignity. The histological type diagnosis was correct in 79 per cent of all tumours. In 94 per cent of the nonmalignant processes the cytological finding was negative; besides, the authors point to the histological diagnosis of several types of benign tumours, Boeck-sarcoidoses, tuberculoses, other granulomatoses etc.