A continuously variable single-tube shock absorber operating according to the skyhook principle and having bidirectional control valves comprises a working cylinder (1), a piston (3) with piston rod (2) which is movable therein, openings (6, 7) cut out in the piston, spring-loaded shock absorber valves (8, 9), fitted on either side of the piston, in order to shut off the openings until a certain fluid pressure has been reached, exciting chambers (12, 13) fitted on either side of the piston and each bounded by a stationary disc (10, 11), a piston skirt (14, 15) which can be slid around such a disc, and a spring-loaded shock absorber valve. The exciting chambers are in communication with a bore (23) in which the pressure is controlled by a control mechanism. Bores (20, 21) through which fluid can flow into the exciting chambers are provided in the stationary discs. The control mechanism can consist of a movable mass which is fitted in a spring-loaded manner and controls the passage of fluid to a bore which is in communication with the exciting chambers, or it can consist of valves to be adjusted by a coil (37).