The electrochemical properties of catecholamines that occur in the haemolymph and cuticle of Manduca sexta (L.) during development were studied. The cyclic voltammetric behaviour for dopamine, N- acetyldopamine (NADA) and N-β-alanyldopamine (NBAD) was similar except that the open chain o- quinones of the latter two compounds cyclized significantly more slowly than dopamine o- quinone . Tyrosinase from pharate pupal cuticle oxidized the three catecholamines with NBAD and NADA being the preferred substrates. Oxidation to the corresponding o- quinone , indolization and reoxidation to p- quinone imine was the pathway observed for both electrochemical and enzyme catalyzed reactions. The possible roles of these metabolites in cuticle sclerotization and melanization are discussed.