This study was performed to validate the combined study of flow radionuclide venography (FRV) with subsequent Tc-99m-red blood cell(RBC) blood pool radionuclide venography(BRV) for the detection of deep vein thrombosis (DVT). Findings in 32 patients with suspected DVT of lower extremities (n = 52) were compared with those of corresponding contrast venograms (CV) serving as a reference method. FRV was performed by using three separate doses of a large Tc-99m04-bolus (10-12 cc) injection. The findings were as follows: concerning the detection of DVT in calf veins, agreement between FRV and CV, FRV$BRV and CV, and BRV and CV were 67%, 73% and 60%, respectively. For femoral veins, agreement between FRV and CV was 96%, while it was 87% between BRV and CV. When FRV and BRV of femoral veins were evaluated in combination, 100% agreement between radionuclide and radiologic methods was observed. For iliac veins there was no disagreement in comparison of the methods either singly or in combination. In 7.6% of the extremities, collaterals not demonstrated by CV and BRV were visualized only by FRV. Although the radioactive agent was injected in a relatively large volume, all of the calf veins could not be filled even when they were completely patent. It was concluded that a combined study of FRV with BRV improved the diagnostic value of radionuclide venography for the detection of DVT in calf and femoral veins.