1. Isolated cases of a dermatitis resembling histologically that of human pellagra have occurred in rats supplied with sufficient vitamin B2 (G) in the form of beef extract or neutral autoclaved yeast to produce good growth.
2. Other rats on basal diets containing similarly prepared nutrients but deprived of any known source of vitamin B2 (G) develop a dermatitis similar in appearance to that described by other workers, but this skin effect differs in histological picture from that found in human pellagra or in black tongue of dogs. These rats showed growth failure which supports the view that they lacked growth-promoting vitamin B2 (G).
3. It is suggested that dermatitis in rats may be of diverse type; one resulting from vitamin B2 (G) deficiency quite different histologically from human pellagra, and one closely allied to human pellagra and black tongue in dogs due to lack of some at present unidentified factor.