Abstract: A horizontal slide mechanism for removably replacing an inking unit in a rotary offset printing press of the type having a plate cylinder, a blanket cylinder and an impression cylinder having parallel rotational axes. The horizontal slide mechanism includes a first guide track and first slide plate mounted to the printing press and to said inking unit adjacent and parallel to the plate, blanket and impression cylinders for guided horizontal movement parallel to the plate, blanket and impression cylinder of the printing press. A second guide track and second slide plate pair are mounted between the printing press and the inking unit at another location parallel to and spaced apart a predeteremined transverse distance from the first guide track and slide plate pair for guided movement and support of the inking unit. A latching mechanism is provided by which the inking unit is releasably held in a first operating position corresponding to inking engagement.