Abstract: In a foldable wheel chair supporting frames for a back, a seat, a pair of back wheels and a pair of front wheels are mutually pivotally connected by means of pivot assemblies positioned at the seat-back junction and comprising a blocking mechanism which is deactuated for releasing the pivotal connection between the supporting frames by turning the seat in a direction of a predetermined reduction of the angular separation between the seat and the back. Each pivot assembly may comprise a pivot pin secured to one supporting frame, and pivot cams secured to the other supporting frames together with an interlocking cam positioned between two of said pivot cams.