A venous occlusion plethysmography using radionuclide (RN) was introduced for the measurement of the limb blood flow. This technique, called RN plethysmography, can be carried out in a subject who has been previously administered RN intravenously for the routine angiographic examination. The blood flow is calculated from the initial slope of the RN count rate change (RN accumulation curve) due to venous occlusion. In this study, this method was compared with electrical admittance plethysmography. The blood flow values determined by these two methods correlated well with each other.