Catheter placement by ultrasound may reduce radiation, improve positioning, and allow the use of echo contrast agents for diagnostic and therapeutic procedures. To evaluate its utility in the peripheral and coronary vascular beds, a preshaped 20 MHz Doppler catheter was inserted into the femoral artery for renal artery, or into the right carotid artery for left coronary artery cannulation in five dogs. Ultrasonic imaging of the vascular structure and catheter was provided by either transabdominal or transesophageal ultrasound. Using Doppler waveform polarity for retrograde guidance, the catheter was advanced to the region of the left renal or left coronary ostia. Ultrasonic emissions from the Doppler catheter were identified by color Doppler mode of the ultrasound machine and allowed the catheter tip to be identified within the beam width of the scanning transducer, providing the depth dimension. In the two animals in which left renal artery cannulation was attempted, the catheter was successfully manipulated into the ostium. In two of the three animals in which left coronary artery cannulation was attempted, the catheter was successfully manipulated into the ostium, followed by saline contrast injections revealing myocardial perfusion. In addition, in one animal, a Doppler flow wire was identified as it was advanced into the mid circumflex coronary. In conclusion, ultrasonically guided cannulation of aortic branches may be possible without x-ray, and this technique may lead to further use of ultrasound in diagnostic and therapeutic procedures.