In a chair comprising a seat frame (6) supported by a frame (2) the seat frame is adjustable as to inclination to occupy a basic position by means of an adjustable pressurized pneumatic spring device (9) to which a pneumatic or hydraulic damper mechanism is connected, said mechanism (11) causing the seat, when occupied, to move slowly away from its basic position, and causing the seat to return quickly to its basic position when the loading ceases or changes considerably. The purpose is to make sitting on the chair less fatiguing.