A feasibility study has been carried out to evaluate rubidium-82, a potassium analog and generator-produced positron emitter, for measuring renal blood flow using a first pass model. Seven acute dogs were studied with beta probes and positron emission tomography to understand the dynamics of rubidium-82 in the kidneys. Preliminary results show that first pass extraction fraction for rubidium-82 ranged from 80-95% with an average of 89%. During the 150 sec of data collection, approximately 44.5% of the injected dose is excreted in the venous side and 9.75% in the ureter. Flow measurements with rubidium-82 and microspheres correlated well with the average control flow of 5.0 ml/min/gm measured by microspheres and 4.5 ml/min/gm of flow measured by rubidium-82 using the first pass model.