Chinoform (7-iodo-5-chloro-8-hydroxyquinoline) which is a derivative of oxin (8-hydroxyquinoline) can chelate with some metals as well as oxin and other derivatives. Applying this principle, the techniques of histochemical demonstration for chinoform, which is probably the causal agent of subacute myelo-optico-neuropathy (SMON), were devised.Copper, iron and silver were used as substances to be chelated with chinoform and they were demonstrated histochemically. In using these techniques, it was necessary to perform these chemical reactions in Tween 80 solution.The possibilities of these techniques were examined using various kinds of materials.Insoluble chinoform hydrolyzed from chinoform glucuronide as a substrate by β-glucuronidase activity deposited ill situ positively and was demonstrated histochemically. In addition, the devised techniques were tested and comparisons were made with the autoradiographic findings in the tissue sections of rabbits to which 131I-chinoform was administered.