The accuracy of Doppler examination was evaluated for the diagnosis of catheter-related venous thrombosis in 40 postoperative patients. Deep vein thrombosis was detected by venography in 15 patients and confirmed by the Doppler technique in a double blind study. Only one false-positive and one false-negative result were obtained with the Doppler technique. This technique appears to be valuable for the early diagnosis of catheter-related vein thrombosis, even in asymptomatic patients.