In emergency traumatology, the iodine 125 labelled fibrinogen test is useful in the early detection of phlebitis in patients in whom the routine use of heparin is not possible--fractures of the cervical spine, severe cranial trauma, elderly subjects. It makes possible the institution of appropriate heparin therapy, without waiting for clinical signs to become evident. We noted that isotopic venous thromboses occured very frequently and very early, and that clinical signs, when present (50 p. cent of cases) occurrer 24 to 48 hours after the appearance of isotopic signs.