HÆMOCHROMOGENS catalyse the oxidation of ascorbic acid at a pH. below 7 at which there is no autoxidation of ascorbic acid. We can confirm this result of Barron and co-workers1, but the authors have overlooked that the hæmochromogens also undergo oxidation under these conditions, as first observed by Karrer and co-workers2. The product of this oxidation is verdohæmochromogen, a bile pigment iron compound3.