The authors start from the fact that till now was a declining attitude in face of the thoracoscopic lung biopsy. Under local anaesthesia any air embolism were happened with it. Moreover there was no optimal instrument for thoracoscopic lung biopsy. Beginning with pressure measurements of the intrathoracic cavity systems the authors research the conditions which can result in air embolism. They found that air embolism is excluded only by unilateral ventilation of the non-biopsied lung of the patient via a channel of Carlens' double-lumen catheter. The other channel of the cathetaer which is connected with the thoracoscopically biopsied lung must be aggreed with the atmosphere in the same way as the pleural space via the open thoracoscope tube. Further it was developed the suction punch, a special instrument for thoracoscopic lung biopsy. In this instrument the proceedings of catch and detache the tissue from the parenchyma are divided contrarily to the forcepslike devices. With this new instrument 63 patients were examined. The thoracoscopic lung biopsy was performed under general anaesthesia with side-separated ventilation through Carlens' catheter. The histologically verified diagnostic yielded was 89 per cent. There aren't serious complications.