A benzylamine oxidase (E.C. 1.4.3.6) has been purified from pig heart. Western blot analysis showed that the enzyme cross-reacts with a polyclonal antibody raised against homogeneous, crystalline pig plasma benzylamine oxidase (BAO). A subunit molecular mass of 97 kDa obtained by SDS electrophoresis is identical to the plasma enzyme. The purification procedure consisted of sequential DEAE-cellulose, DEAE-Sephadex, Con A-Sepharose, Sephadex G 200 and hydroxyapatite columns. The specific activity of the purified enzyme was 0.037 µmol min-1mg-1 at 37uC and the Km for benzylamine was estimated to be 29 µM. The enzyme was inhibited by carbonyl reagents such as semicarbazide and a-aminoguanidine. Phenylhydrazine reacts mole to mole with the enzyme giving a peak at 425 nm. The copper content was 2 g-atom/mole of enzyme.