New derivatives of 2-propinyl amine were studied as possible inhibitors of mitochondrial monoamine oxidases (MAO) from rat liver and brain tissues. Kinetics of inhibition of the MAO activity (A and B types) is described for one of the substances studied -- N-(8-quinolyl methyl)-N-methyl-2-propinyl amine. Interaction of N-(8-quinolylmethyl)-N-methyl-2-propinyl amine with MAO of the A type (serotonin as a substrate) and of the B type (beta-phenylethylamine as a substrate) was studied by the kinetic method, which enabled to determine and quantitatively estimate the steps of enzyme-inhibitor complexes formation. The inhibition of the mitochondrial MAO A and B types by the substance was shown to include the steps of formation of dissociating enzyme-inhibitor intermediates with the subsequent irreversible modification of them. The data on K1 values, estimated in experiments with serotonin and beta-phenylethylamine as substrates, show that the affinity of N-(8-quinolyl methyl)-N-methyl-2-propinyl amine towards MAO of the A type was 10-fold higher than the affinity towards MAO of the B type. The rates of these complexes conversion into irreversibly blocked forms of the MAO A and B types was found to be similar.