DURING the enzymic oxidation of catechol, approximately two atoms of oxygen are taken up for each molecule of catechol, whereas only one atom is required for oxidation to the o-quinone stage. Wagreich and Nelson1 consider this extra uptake to be accounted for by the interaction of the o-benz-quinone with water to form 1 : 2 : 4-trihydroxy-benzene, which then reacts with a further molecule of o-benzquinone to produce hydroxy o-quinone and a molecule of catechol. Their evidence that a poly-phenol is produced from o-benzquinone, capable of being oxidized to an o-quinone by tyrosinase, is convincing. That the polyphenol produced is identical with catechol cannot be taken as established. The scheme has also been strongly criticized by Wright and Mason2.