REPORTS HAVE RECENTLY appeared describing a peculiar hepatotoxic effect in mice fed large doses of the antifungal antibiotic griseofulvin.1,2In these studies, in addition to hepatocellular changes, evidence of a marked disturbance in hepatic pyrrole and porphyrin pigment metabolism was present. With these results in mind, we have investigated the effect of ordinary therapeutic doses of griseofulvin in two patients with an inborn error of pyrrole pigment metabolism, acute intermittent porphyria. The subjects of this study were two patients with acute porphyria in clinical remission. Patient 1 was a 31-year-old man who had suffered his first attack of clinical porphyria in July, 1958, and had suffered four distinct acute attacks since. In each instance, the urine contained large amounts of porphobilinogen (Ehrlich aldehyde complex insoluble in chloroform and butyl alcohol), and variable increases in uroporphyrin. Fecal porphyrin excretion was determined during two acute episodes, revealing increased fecal excretion of