Abstract: A plate lockup mechanism secures a printing plate to a printing cylinder. The mechanism includes two movable members disposed within the printing cylinder. Means connected with one of said members engages one end portion of the printing plate to secure the one end portion of the plate on the cylinder and means connected with the other of said members secures the other end of the plate to the cylinder. Each of the members is movable between first and second extreme positions. A biasing spring coacts between the two members and urges one of the members to either one of its extreme positions when the other member is in its first extreme position and when the other member is in its second extreme position.