Biogenic amines play key roles in neurotransmission, metabolism, and in control of various physiological processes.  Using a variety of synthetic methodologies, including novel procedures developed by us, we have prepared a series of biogenic amines with fluorine substituted at various ring-positions.  By virtue of its very small size and high electronegativity, fluorine is a very favorable replacement for hydrogen in these analogs.  The biological properties and usefulness of these ring-fluorinated biogenic amines have proved to be extremely rewarding and continue to find applications in a multitude of studies, including research on the mechanisms of transport, storage, release, metabolism, and modes of action of these amines.  Of particular significance was the discovery that 6-fluoronorepinephrine is a selective, alpha-adrenergic agonist and 2-fluoronorepinephrine is a selective beta-adrenergic agonist.  Mechanisms considered to explain these results include: 1) a direct effect of the C-F bond on agonist-receptor interaction or 2) an indirect effect of the C-F bond on the conformation of the ethanolamine side-chain.  The results of testing of new analogs synthesized to probe these mechanisms indicate that electronic effects may be more important than conformational factors.  Fluorinated analogs are useful biological tracers.  For example, [18 F]-labeled 6-fluorodopamine, the biological precursor to 6-fluoronorepinephrine, has been found to be an excellent scanning agent for peripheral noradrenergic innervation.