An energizer for use with a guidewire, such as a vascular guidewire, in one embodiment engages a proximal end of the guidewire and applies energy to be transmitted to a distal portion of the guidewire. A jack or other receptacle accommodates, in a releasably secured fashion, a proximal portion of the guidewire having a diameter that is not substantially larger than, but preferably is equal to or less than, the maximal diameter associated with the guidewire. The jack may be structured so that designated portions of the proximal end of the guidewire will be disposed in selective contact with corresponding portions of the jack in order to permit, for example, an electrical potential to be applied across such portions, thereby energizing an electrically controllable part of the guidewire, such as a steering mechanism. In this manner, the energizer permits rapid engagement and disengagement of a proximal portion of the guidewire. Equipment such as catheters may conveniently be fed coaxially over the proximal portion of the guidewire and up toward the distal end and conveniently exchanged with reduced complexity of, and disturbance to, the guidewire, its environment, and the energizing mechanism.