Scott, W. M. (Wayne State University, Detroit, Mich.), R. C. Burgus, J. B. Hufham, and J. J. Pfiffner. Microbial degradation of corrinoids. I. Vitamin B(12). J. Bacteriol. 88:581-585. 1964.-Microorganisms isolated from a variety of soil, sewage, and mud samples, and stock cultures, were examined for the ability to degrade vitamin B(12). More than 200 isolates which attack the vitamin were examined, and they all demonstrated reversible fading of the red vitamin. The color was restored by aeration. Very few microorganisms were able to degrade the vitamin to permanently colorless products, although many were able to degrade it partially, to produce new pigments. Some of these pigments appeared similar, if not identical, although they were produced by different bacteria. Radiotracer and electrophoretic mobility data are presented to show that the transformation products are derived from the vitamin. All the degradative microorganisms isolated were bacteria, and the most active was Pseudomonas rubescens.