Many of the trace amines-more correctly called biogenic amines have been known for decades, but because of their tiny concentra tions (0. 01-100 ng/g) in brain, it was only after the development of sophisticated analytical techniques (such as mass spectrometry) that they could be identified and quantitated in nervous tissue. There are now more than 20 of them and most are related to the catecholamines and 5-hydroxytryptamine both structurally and metabolically. Their pharmacological and physiological properties make them prime candidates for a transmitter or neuromodulator role and many of...