Abstract: A mechanism for adjusting the position of the side support panels of a seat back comprises a pair of projecting side frame members which are secured at one end against rotation relative to the seat back frame. At least that portion of each side frame member near to the attached end is made of spring steel, so that side frame members can be cantilevered toward or away from one another, against the force of the spring steel, about axes which are substantially parallel to one another. Preferably, each side frame member has a generally U-shaped configuration so as to have a pair of generally parallel legs and terminates in end portions which are fixedly secured relative to said seat back frame. In a preferred embodiment, each end portion includes a first end portion perpendicular to the leg portion, a second end portion which extends from the first end portion at least generally parallel to the leg portion, and a third end portion which extends at least generally parallel to the first end portion.