The potential advantage of using 111In-antifibrin (111In-AF) monoclonal antibody for the diagnosis of deep venous thrombosis (DVT) was studied in 44 patients with suspected DVT (27 underwent heparin therapy before 111In-AF injection). All patients had contrast venography (considered as the gold standard) and 111In-AF scintigraphy within 24 hr. Two to 3 mCi of 111In-AF were injected intravenously, and planar scintigraphy of the limbs was recorded within 10 min (17 times), 3 hr (44 times), and 18 hr (39 times). Indium-111-AF images were then interpreted without knowledge of the results of the other examinations. The DVT diagnostic accuracy of 111In-AF was greater when interpretation was based on images recorded at different time periods after injection. Indium-111-AF sensitivity for diagnosis of DVT was 85% (29/34) and was not apparently decreased by heparin therapy. None of the 10 patients with negative contrast venography had a positive 111In-AF scan. The results demonstrate the importance of recording serial images and the excellent accuracy of 111In-AF for diagnosing DVT.