Summary and Conclusions 1. These studies confirm the previous observations of Beckh, Ellinger and Spies1 that porphyrinuria is a frequent finding in pellagra and disappears following the administration of yeast. 2. The present study shows that nicotinic acid, a substance which has been shown to be curative for the mucous membrane lesions of pellagra, likewise produces a decrease of porphyrinuria in pellagrins. 3. In addition, the present study shows that the porphyrinuria associated with a number of diseases other than pellagra likewise is promptly decreased following the administration of either yeast or nicotinic acid.