Abstract: An improved mechanism for adjusting the angle of inclination of the back-rest of a seat includes an elongated support arm for the back-rest, pivoted in the region of its lower end upon a transverse, generally horizontal pivot, a pair of complementary cams which are in relatively fixed relationship with each other and which abut the support arm on its opposite sides and on opposite sides of the pivot, and a screw mechanism for moving the cams in a direction transverse to the length of the support cam.