For the development of amino acid derivatives as a new pancreas-scanning agent, comparative experiments were made on the in vivo incorporation of 18 kinds of 14C-labeled L-amino acid, and of D- and DL-forms of 4 selected radioactive amino acids into the trichloroacetic acid (TCA)-soluble and protein fractions of the pancreas and liver of mice. Among the L-forms tested, tryptophan, valine, methionine and leucine, in this order of decreasing incorporation, showed a relatively high incorporation into the pancreas 30 min after i.v. injection. Pancreas/liver ratio of the radioactivity of methionine, valine and leucine determined 15, 30 and 60 min after injection was 6:10. Although all of the amino acids were not predominantly high in the pancreas/liver ratio compared with selenomethionine-75Se, the 3 amino acids seem a possible mother compound for introducing .gamma.-emitters as a pancreas-scanning agent. In the TCA-soluble fraction of the pancreas, radioactivity of DL- or D-amino acids tested was higher than that of the corresponding L-amino acid. Almost all of the radioactivity of D-leucine was found in the TCA-soluble fraction. The incorporation of D-leucine into the pancreas was much the same as L-leucine. .gamma.-Radiating derivatives of amino acids might be useful as a new pancreas-scanning agent.