Abstract: This device relates to an adjustment mechanism for adjusting the angular positions of a seat and a back rest of a chair. The mechanism comprises a fixed horizontal beam having a seat support member pivotally connected thereto by a transverse pivot adjacent one end of the beam and a back support member pivotally connected to the seat support member by a second transverse pivot. Opposed adjacent ends of the fixed beam and the back support member have spaced plates fixed at their adjacent ends with elongate aligned apertures. Locking means are mounted on the seat support member extending through the aligned apertures for locking the plates on the seat support member and the back support member into selected angular positions with respect to the horizontal beam.