Tissue distribution of 99mTc-1-thioglucose was studied in inbred albino Fisher rats. High levels of radioactivity were observed in the kidney with concurrent low pancreatic levels and pancreas/liver ratios of 0.4 following intravenous administration of the agent. High pancreatic concentration were observed with pancreas/liver ratios of 4.0 after intraperitoneal administrations. Future studies on pancreatic radiopharmaceuticals should avoid production of artificially high pancreatic values by intraperitoneal injection.