In order to evaluate the usefulness of B-mode ultrasonography in the diagnosis of deep vein thrombosis, a prospective study was performed on 145 patients. Each patient was examined with occlusive venous plethysmography, continuous wave Doppler, real-time B-mode ultrasonography, and radiographic contrast phlebography. The diagnostic sensitivity and specificity versus phlebography were 91 and 82.1 per cent, respectively, for plethysmography, 92 and 86.6 per cent for Doppler, and 94 and 100 per cent for B-mode sonographic scanning. The combined noninvasive approach reached a 96 per cent sensitivity. B-mode ultrasonography demonstrated a mass in eight cases, and showed a superficial venous thrombosis in four cases, among the 45 patients without deep vein thrombosis. B-mode ultrasonography, therefore, appears to be very useful in obtaining a better specificity and differential diagnosis.