After proper insertion of an intact leftsided Robertshaw endotracheal tube an acute block of the right main bronchus occurred in two patients. The cause was seen in too short a distance between the upper tracheal and the lower bronchial cuff of the tube. In case of a greater distance between the cuff-bearing segments this problem was never encountered. A careful measurement of all Robertshaw tubes demonstrated segments of various length between the upper and lower cuffs. Information from the manufacturer Malinckrodt New York/Grossostheim revealed that this problem has been solved by standardized segments of greater length. Also the Portex company Hythe/Hamburg appears to be aware of this problem.