An enzyme capable of cleaving catechin was present in the mycelium ofCheatomium cupreum. Maximum synthesis of the enzyme occurred after 15 days growth. Sucrose and maltose increased enzyme synthesis among the carbon sources tested. Catechol, protocatechuic acid and phloroglucinol carboxylic acid were the intermediates of catechin degradation.Cheatomium cupreum containedmeta-cleaving enzymes for catechol and protocatechuic acid metabolism. Pyruvate was identified as an end-product. Catechin oxygenase from the mycelium ofC. cupreum was purified to homogeneity. It was optimum at pH 7.0 and 50°C and was highly specific for catechin, with a Km of 4 μM. Its molecular size was 40 kDa, as determined by gel filtration and gel electrophoresis, and it had a pI of 9.1.p-Chloromercuric benzoate, iodoacetate, N-ethylmaleimide, 2,2'-dipyridyl and EDTA markedly inhibited the enzyme activity. It was a glycoprotein.