In four patients with liver disease (fatty liver, fibrosis, and cirrhosis) the concentrations of uroporphyrin and heptacarboxylic porphyrin in the liver were found to be considerably elevated (up to 90 µg/g). The patients also excreted increased amounts of porphyrin with the urine (0.5–1 mg/l), although cutaneous symptoms were not present. The constellation of urinary porphyrins differed from that in chronic hepatic porphyria Types A and B, but was similar to that characteristic ofporphyria cutanea tarda. The relative proportion of heptacarboxylic porphyrin in the liver is, however, 50% lower than that inporphyria cutanea tarda. The biochemical abnormality found in these four patients is given the name of chronic hepatic porphyria type C. Fasting, glycine loading, alcohol, and high fat diet bring about an increase in porphyrin excretion.