An optical stylet was developed which can be inserted into an endotracheal tube, and the passage through the vocal cords and position of the cuff in the trachea could be controlled visually. It is of great help in difficult intubations in adults and children. It became an invaluable tool in teaching endotracheal intubation by coupling a teaching attachment (beam splitter) to theoptical system. The operator and the second observer (student) can see the actual manipulations simultaneously.