125I fibrinogen test was performed in 20 selected patients who presented with symptoms suggestive of deep venous thrombosis. The incidence of a false positive study was found to be very high: 90%. An increased accumulation of fibrinogen was noted over recent, well-healed surgical incisions, diffuse or focal inflammatory sites, hematoma and also, following a venogram or arthrogram test. The large number of coincidental circumstances that result in an abnormal accumulation of 125I fibrinogen lead us to believe that venogram is the procedure of choice in patients with symptoms simulating thrombophlebitis.