Abstract: An apparatus for exchanging over-the-wire balloon catheters engages a guide wire within a guide catheter. In one embodiment the engagement is by an inflatable balloon in the guide catheter. Alternatively, the engagement is accomplished by a captivation wire in the guide catheter that has a collapsible loop portion through which the guide wire extends. Inflation of the balloon or closing the loop portion of the captivation wire within the guide catheter traps the guide wire and restricts its movement relative to the guide catheter. Once the guide wire position is fixed, withdrawal of a first balloon catheter and subsequent introduction of a second balloon catheter over the guide wire is possible without moving the guide wire longitudinally. Thus, the positioning of the guide wire over a stenosis to be dilated is not disturbed.