Structure-activity relationships were performed on a new series of thiazole derivatives which selectively inactivate monoamine oxidase-B (MAO-B), purified from mitochondrial beef liver. All of the synthesized and tested compounds showed non-competitive inhibition, suggesting the formation of a stable adduct between the tertiary amine function, linked to the thiazolyl derivatives and the active site of the enzyme. The mechanism of MAO-B inhibition is discussed in terms of the Ionization Potential of the amine nitrogen atom and the conformational flexibility of the inhibitors.