A histochemical method for staining CNS zinc by the stoichiometric formation of zinc: quinoline fluorescent chelates is described. Four congeners of quinoline have been tested, and two found to be useful for histochemistry. The procedure is a one-step method, suitable for fresh-frozen and fixed tissue sections alike. The quinoline fluorescence selectively labels the CNS regions (such as hippocampus, amygdala) shown by prior histochemical procedures to be rich in histochemically reactive zinc in axon boutons and therefore appears to be a specific marker for the bouton zinc. Microfluorometric data indicate that the fluorochrome can be used for quantitative estimates of CNS zinc pools as well as qualitative studies of localization.