Some parameters of iron metabolism in 26 patients with porphyria cutanea tarda (PCT) which is often associated with mild iron overload and hepatic siderosis, are studied. Serum iron, percent transferrin saturation and ferritin were pathologically increased. Statistical comparisons were performed between PCT patients and healthy controls, liver disease patients (cirrhosis, chronic active hepatitis) and patients with associated liver siderosis (alcoholic cirrhosis, cirrhosis and chronic active hepatitis in thalassemia). Ferritin levels are higher in patients with porphyria than in healthy controls (p less than 0,001) and in patients without liver siderosis (p less than 0,001). No statistical difference is observed between patients with porphyria and patients with siderosis. A significant decrease in ferritin levels is registered after venesection therapy. The conclusion is drawn that serum ferritin increase in PCT is related to hepatic iron store amounts rather than hepatic necrosis. It is assumed that ferritin follow-up during phlebotomy therapy and also during remission is useful to indicate the exhaustion or an early replenishment of hepatic iron stores.