One of the major unresolved problems in the development of laser angioplasty is in monitoring the process of plaque ablation in real-time to provide the necessary operator feedback. As part of a project to test the feasibility of intravascular imaging with ultrasound we have developed, constructed, and tested a 20 MHz transmitter/receiver which can detect echoes from transducers small enough to fit on a 3-F (1 mm diameter) catheter. Resolution with a small aperture (0.5 x 1.0 mm) focused transducer is about 0.25 mm in both axial and longitudinal directions at 1.5 to 6.0 mm from the transducer face. Images of arteries made in the laboratory with a simple rotational scanner have sufficient resolution to show lumen size and geometry, wall thickness, branches, and craters caused by laser ablation. From these initial studies intravascular ultrasonic imaging appears feasible.