We validated a novel non-invasive radionuclide plethysmography technique to evaluate peripheral arterial blood flow. This method, based on the measurement of blood volume variations during repetitive venous occlusions, was compared to strain gauge venous impedance plethysmography. The technique uses 99m-technetium labeled autologous red blood cells scintigraphy to determine the rate of change of forearm scintigraphic counts during venous occlusion. Thirteen subjects were simultaneously evaluated with radionuclide and impedance plethysmography. Six baseline flow measurements were performed to evaluate the reproducibility of each method. Twenty-seven serial measurements were then made to evaluate flow variation during forearm reactive hyperemia. After 30 min of recovery, resting forearm blood flows were again evaluated. Impedance and radionuclide methods showed excellent reproducibility with intraclass correlation coefficients of 0.96 and 0.93 respectively. There was also good correlation of flows between both methods during reactive hyperemia (r = 0.87). Resting flows at 30 min post reactive hyperemia were slightly lower than baseline with both methods. We concluded that radionuclide plethysmography could be used for the non-invasive evaluation of forearm blood flow and its dynamic variations during reactive hyperemia.