Fluorinated analogs of norepinephrine, isoproterenol, phenylephrine, tyramine, dopamine, melatonin, serotonin, DOPA, Alpha-methyl DOPA and reserpine have been synthesized. Biochemical and biophysical studies on these analogs have revealed important information concerning structural requirements for norepinephrine in interaction with Alpha- and Beta-adrenergic receptors, and the role of phenolic pK and lipophilicity in determining activity of biogenic amines.