Abstract: A retraction mechanism is disclosed for retracting and engaging the pumping mechanism assembly of an infusion pump with an infusate flow path. The retraction mechanism provides a linkage which converts rotary motion of a handle about an axis to linear motion along a line parallel to the axis. The linkage is connected to the pumping mechanism assembly to cause the pumping mechanism assembly to retract from or engage with the flow path via a disposable cassette. The retraction mechanism is biassed toward the engaged position to prevent free flow of infusates on the flow path. The retraction mechanism is operable in two steps: first, the handle is pulled out against the biassing force; second, the handle is rotated until it locks into the retracted position. The mechanism includes a toggle linkage which aids in locking the mechanism in the retracted position and in biassing the mechanism to the engaged position when the handle is moved out of the locked retraction position.