selectively inhibit monoamineoxidase (MAO) by in‐vitro tests. Monoamineoxidase was isolated and purified from the mitochondrial extracts of rat‐liver homogenates and human platelets. Monoamineoxidaseinhibitoryactivities of the compounds were compared with pargyline and clorgyline. Most of the compounds inhibited the total activity of rat liver homogenates. The monoamineoxidase‐A inhibitory effects of