Hydroxocobalamin was found to be as effective as cyanocobalamin on the growth of Ochromonas as well as on Lactobacillus leichmannii. When it is autoclaved with the Ford medium at 120° for 10 minutes, it is decomposed and the activity was reduced to as low as 20 per cent, and it is not reproducible. In order to determine hydroxocobalamin it is necessary to add it aseptically to the sterilized medium or to autoclave with stabilizing agents such as ascorbic acid.
