Unlike the related noncyclic amidines which are broad-spectrum cestocides, a number of 2-imidazolines substituted in the 2 position by alkoxyaryl groups were not highly active in screening tests against the mouse tapeworms Hymenolepsis nana and Oochoristica symmetrica. Certain of the 2-(4-alkoxynaphthyl)-2-imidazolines and 2-(6-alkoxy-2-naphthyl)-2-imidzolines, however, had activity interpreted as antidepressant in the mouse. This activity paralleled in vitro irreversible inhibitory activity against mouse brain MAO for those where no substitution is present on the imidazoline ring. This irreversibility probably has a different origin from that postulated to explain the irreversible MAO inhibition of proparglic, cyclopropyl, and other "chemically reactive" MAO inhibitors.