1. Kryptopyrrole (2,4-dimethyl-3-ethyl pyrrole) was shown to elevate the urinary porphyrin excretion and the hepatic content of porphyrins in the rat. The simultaneous administration of δ-aminolaevulinic acid increased these effects.
2. Kryptopyrrole was present in the urine of patients with hereditary hepatic porphyria, in attack and in remission, but not in those with latent porphyria.