In 318 patients screening for the development of postoperative deep vein thrombosis was made with the 125I-fibrinogen test. In addition to the conventional measurements over the leg the planta pedis was also included. Of 221 legs with thrombosis 75 had an increased uptake in the planta pedis, but only in sixteen patients an isolated plantar thrombosis was found. In only eight of 70 thrombi there was evidence of a proximal extension of the plantar vein thrombosis. The time for the thrombosis debut did not differ between isolated plantar vein thrombi and more extensive thrombi; the majority beginning during the first four postoperative days.