A coupled peroxidation technique for localization of monoamine oxidase (MAO-A and MAO-B), applied to post-mortem fixed tissue of the locus coeruleus of the Mongolian gerbil is demonstrated. Tyramine hydrochloride, beta-phenylethylamine and 5-hydroxytryptamine creatinine sulphate were used as substrates, 1-deprenyl and clorgyline served as specific inhibitors. All three substrates stained the neurons of locus coeruleus in the absence of inhibitor. In the presence of 1-deprenyl, tyramine hydrochloride and 5-hydroxytryptamine creatinine sulphate were metabolized, whereas in the presence of clorgyline no reaction with either substrate could be observed. Immunocytochemical staining of tyrosine hydroxylase (TH) was employed as comparison.