Abstract
1 . Data has been presented showing that tetrazolium salts can be used for the histochemical localization of monoamine oxidase, although there are limitations to its application to in vitro studies. These limitations have been discussed.
2. It appears that an indole carbonyl compound is necessary for 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride reduction. A diaphorasetype system may be required to transfer the electrons from the indole carbonyl intermediate to INT.