With recent advances in instrumentation (1) and the development of new localizing materials, isotope scanning has been applied to the visualization of lesions of the thyroid, kidneys, brain, liver, spleen, and bone. The addition of the pancreas to this growing list has awaited the development of a suitably labeled pancreas-specific compound. We have previously reported (2) animal distribution studies of a new agent, Se75-selenomethionine, with sufficient pancreas specificity to be useful for scanning. The present report deals with the clinical applications of this compound. The pancreas uptake of amino acids has been recognized for some time (3). This uptake is a reflection of the rapid rate of synthesis of the digestive enzymes. From 5 to 10 per cent of most amino acids are found in the pancreas within an hour after administration. Unfortunately none of the elements in the structure of amino acids (C, H, N, O, and S) have isotopes with properties suitable for scanning. Externally labeled amino acids (e.g., I131-iodotyrosine), because of their inability to take part in protein synthesis, show no pancreatic uptake. The chemical similarity of selenium and sulfur is so close that the substitution of Se75 for sulfur within a methionine molecule results in an analog which has all the properties of amino acids (2, 4), including incorporation into proteins. The physical properties of Se75 (half-life, 128 days; principal γ ray, 0.27 Mev) are well suited to scanning. Using Se75-selenomethionine prepared by yeast biosynthesis (5), we have scanned more than 50 patients. Since the pancreatic tissue itself is not labeled, a protocol must be used which favors enzyme synthesis within the pancreas but avoids any stimulus which would cause pancreatic secretion. In addition, it appears that prolonged food deprivation (overnight or longer) favors uptake in the liver. We have temporarily adopted the following procedure: Three to four hours following a high protein break fast, the pancreas is stimulated to empty by a dose of mixed secretin and pancreozymin (Cecekin Vitrum); one hour later, 3 to 3.5 rnicrocuries/kilogram of Se75-selenomethionine are given intravenously, and scanning is started one half hour after injection. We have been able to visualize the pancreas in about two-thirds of the patients scanned. To date, no scans have been done on patients with known pancreatic disease. The estimated dose to the patient from this procedure is about 0.6 rad, total body, delivered over several months. In Figure 1 are reproduced two selected photoscans showing good pancreas visualization. The densities in the upper left hand corner represent the thick portions of the liver. It seems possible that space-occupying pancreatic lesions 2 cm. or more in diameter could be visualized as nonfunctioning areas of decreased uptake on scans of this type.