The aim of this study was to characterize modified Technegas, employing radiochemical analyses and qualitative rabbit organ imaging techniques. Electrophoresis, thin layer chromatography and imaging studies, found modified Technegas to behave like sodium [99mTc]pertechnetate (pertechnetate). Our data indicate that modified Technegas is a pertechnetate aerosol, which results from the presence of 3% oxygen in the reaction atmosphere of the Technegas generator.