An endobronchial tube assembly for selective ventilation of the left or right lung has an endobronchial tube (1) with two passages opening into the left and right lungs. A selector (2) mounted at the machine end (20) of the tube (1) has a rotatable plate (70) with apertures (73, 74, 75) which can be positioned to allow gas to flow along a selected passage of the tube (1). A lock mechanism (90, 81, 82, 83) retains the plate (70) in the selected position until a button (61) is depressed to release the plate, which can then be moved to one side or the other by displacing a knob (77).
