Abstract: A collapsible convertible top or roof for motor vehicles has a linkage system including a front roof frame, a rear roof frame, a main roof arch, a two-part retaining rod supporting the roof arch against a tension bracket, and a linkage for displacing the roof frames and parts of the retaining rod between an extended position and a collapsed position. To assure stability of the linkage system with the convertible top in the extended or closed position, a locking mechanism is provided including a pivotal locking bar displaceable between a locked position and a released position by an actuating lever moved in accordance with the operation of the convertible top or roof. The actuating lever is mounted on one of two cooperating parts and pivots about an axis parallel to an articulation axis of the parts. A catch cooperates with the locking bar for securing the extended position.