Renal tumor vasculature can be detected by monitoring the kidneys with the gamma-ray scintillation camera following a rapid intravenous injection of Tc99m pertechnetate. It is, therefore, possible to distinguish neoplasm from cyst or ischemia. Some of the limitations of this modality are discussed. Its advantages as another screening procedure are that it is rapid, innocuous, requires no patient preparation, is free of interference from gas and fecal material, and gives low radiation exposure.