A method and apparatus for combining therapeutic pulsed or continuous-wave ultrasound with diagnostic pulsed ultrasound are described. In both a therapeutic mode and in a diagnostic mode, the ultrasound is administered from a single probe to a patient suffering from thrombosis. The ultrasound can have the same or different frequency ranges in the diagnostic and therapeutic modes. The pulsed or continuous-wave ultrasound in the therapeutic mode enhances a lysing effect of a thrombolytic agent. The pulsed ultrasound in the diagnostic mode allows monitoring of blood flow to locate a thrombus, to determine an optimal window to administer the therapeutic pulsed ultrasound, and to detect when recanalization has occurred. If an operator attends the device, a graphical display operates during the diagnostic mode to display an image representative of the blood flow.