Growth studies indicate that ammonium compounds are preferred inorganic N sources for M. purpureus, and that nitrites are better than nitrates. Each of several amino acids (e.g., glycine, leucine, valine, aspartic acid, glutamic acid, arginine) and urea were found equal or superior to ammonium salts as a sole source of N. The addition of Zn to the media resulted in increased growth regardless of the N source. The data presented indicate the involvement of Zn in interrelationships between carbohydrate and N metabolism during growth.