Obstructive lesions of the larynx and subglottic space are always a challenging problem for the endoscopist and anaesthetist. At this level, the efficacy and innocuity of a carbon dioxide laser treatment are related to the degree of endoscopic exposure. Thanks to the transtracheal high frequency jet ventilator, it is now possible to assure a free laryngeal endoscopic operative field. The transtracheal catheter is introduced percutaneously through the cricothyroid membrane into the trachea under endoscopic control and connected to a high frequency jet ventilator. From November 1983 to April 1985, this technique has been used in 65 cases. In 12 cases, it was the only alternative to avoid a tracheostomy. The other indications were: laryngeal papillomatosis, resection of T1a cancers of the vocal cords, fibrous strictures secondary to long term intubation, laser arytenoidectomies and benign lesions of the vocal cords. Among many advantages, the following are the most convincing: clear vision of the operative field for the surgeon, complete relaxation of the patient, good respiratory gas exchange, elimination of the risk of ignition of an endotracheal tube by laser, decreased risks of broncho-aspiration of blood and debris, and the facility to provide oxygen and/or mechanical ventilation in the postoperative period. The only complication encountered was a case of cervico-mediastinal emphysema caused by displacement of the tracheal catheter.