The role of contact B-mode ultrasonography in demonstrating prosthetic vascular grafts was assessed in 24 patients (27 grafts). All grafts were well delineated. End-to-side bypass grafts could be separated from end-to-end replacement grafts by their characteristic appearance. Patent and occluded grafts could not be distinguished either in vivo or in vitro. However, B-mode ultrasonography was ideally suited to the detection of other complications of vascular prosthetic grafts: hematoma, infection, and false aneurysm formation.