This invention is a single-lumen balloon catheter having a valve seat on the distal end of the catheter, distal of the balloon, which may be operated by a control wire having a valve plug disposed on the wire. The valve seat may be engaged by the valve plug from either direction, depending on the installation of the control wire. In either event, if the valve plug is installed distally of the valve seat in the catheter lumen, the valve is closed by pulling on the control wire (or moving the control wire in a proximal direction) and introducing fluid through the catheter lumen through the balloon. Alternatively, the guidewire, with its integral valve plug, may be introduced from the proximal end of the catheter and may traverse the body of the balloon to engage the valve seat in the distal end of the catheter. Pushing on the control wire will seat the valve, allowing the introduction of fluid through the catheter lumen to inflate the balloon. The latter arrangement allows the control wire to be interchanged with other guidewires a physician may wish to use. The balloon provided for in this invention is of a single length and does not change its axial length as it is inflated.