Abstract: A two-color offset printing press having two plate cylinders simultaneously engageable with a single blanket cylinder is disclosed. The plate cylinders and the blanket cylinder are rotatably mounted on a printer head fixed to the mainframe of the press. A first set of dampening and inking rollers is mounted on the printer head and engageable with one of the plate cylinders. A second set of dampening and inking rollers, engageable with the other plate cylinder, is mounted on a ball bushing supported carriage linearly movable to and from the printer head along a pair of parallel rails fixed to the mainframe. Image registry between the two plate cylinders is established by an operator-accessible adjustment mechanism for shifting one of the plate cylinders back and forth along its axis of rotation. An electrical safety interlock system precludes operator access to the carriage-associated plate cylinder during predetermined operating modes of the press.