Seventeen 2-aryl-3-haloallylamine derivatives were prepared and evaluated as inhibitors of monoamine oxidase (MAO, EC 1.4.3.4). The synthesis of these compounds was achieved from either .alpha.-methylstyrene or ring-substituted phenylacetic acid derivatives. With 1 exception, these 2-arylallylamines [2-phenylallylamine, (E)-2-phenyl-3-chloroallylamine, (Z)-2-phenyl-3-choloroallylamine, (E)-2-phenyl-3-bromoallylamine, 2-phenyl-3,3-dibromoallylamine, (E)-2-(3,4-dimethoxyphenyl)-3-fluoroallylamine, 2-phenyl-3,3-difluoroallylamine and (E)-2-(3,4-dihydroxyphenyl)-3-fluoroallylamine] were enzyme-activated, irreversible inhibitors of MAO. The most potent inhibitors were ring-substituted derivatives of (E)-2-phenyl-3-fluoroallylamine with IC50 [median inhibitory concentration] values ranging from 10-6-10-8 M. Selectivity for the A and B form of MAO depended on the nature of aromatic ring substitution. In general, hydroxyl substitution favored the inactivation of the A form of MAO, while very selective B inhibitors were obtained when the aromatic ring was substituted with a 4-methoxy group. (E)-2-(4-Methoxyphenyl)-3-fluoroallylamine and (E)-2-(3,4-dimethoxyphenyl)-3-fluorallylamine proved to be in vitro as selective for the B form of MAO as deprenyl. [MAO inhibitors are used in the treatment of depression and certain forms of phobic anxiety and have occasionally been used in the treatment of hypertension.].