Summary Sulfanilamide, replacing p-aminobenzoic acid in a synthetic diet containing 7 B complex factors including inosi-tol, prevents the development of the syndrome heretofore associated with a deficiency of p-aminobenzoic acid, but it does not entirely replace p-aminobenzoic acid. Intestinal antiseptics (sulfonamides and aseptoform) added to synthetic diets containing 8 B complex factors make possible the demonstration in rats of a deficiency syndrome which it is suggested may be due to a ninth B complex factor.∗