A series of 15 alpha-allenic amines, including primary, secondary, and tertiary ones, was synthesized, partly by organocopper chemistry. Their ability to inhibit mouse and rat brain mitochondrial monoamine oxidase (MAO) in vivo and in vitro, respectively, was evaluated. Almost all compounds were quite potent inhibitors of MAO, some as potent as deprenyl. Like deprenyl, most of the compounds were selective inhibitors of the B form of MAO. the two enantiomeric forms of N-methyl-N-(2,3-pentadienyl)benzylamine (2) were prepared and the R-(-) form was found to be 2.7 times as active as the (+) form in vivo and 25 times as active in vitro. Most of the compounds were tested for their ability to potentiate the phenylethylamine (PEA) response in mice, and a good correlation between the potency of MAO inhibition and PEA potentiation was found. Compound 5, as the only compound tested, did not potentiate the blood pressure response to tyramine.