Venography is the standard method for the diagnosis of venous thrombosis but is invasive and may cause discomfort. We evaluated the combination of impedance plethysmography and 125I-fibrinogen leg scanning as an alternative to venography in 200 symptomatic patients. One or both of these less invasive tests was positive in 81 of 86 patients with positive venograms (sensitivity of 94 per cent) and both were negative in 104 of 114 patients with negative venograms (specificity of 91 per cent). These two tests detected all 60 patients with popliteal or more proximal venous thrombosis and 21 of 26 patients with calf-vein thrombosis. In addition, this approach detected 21 of 22 patients with calf-vein thrombosis with symptoms for eight days or less. These results suggest that the combination of these two less invasive tests can be used as an alternative to venography in selected patients with clinically suspected venous thrombosis.