Iron kinetics, absorption and storage were studied by means of 59Fe and deferoxamine (Desferal-Ciba) in eight patients with porphyria cutanea tarda at the time of clinical activity and after allopurinol treatment. At the time of clinical manifestations, a significant impairment of erythrocyte-iron turnover and of radio-iron utilization was demonstrable in a half of the patients and a significant increase in iron absorption and turnover in patients out of 8. The measurements of surface activity in vivo showed a significant increase in storage iron. This was confirmed by the excessive urinary excretion of deferoxamine-iron, attaining three- to four-fold figures of the normal values (251 +/- 85 mg). The increased absorption of iron coupled with an abnormal porphyrin metabolism is suggestive of a double genetic defect. As a result of allopurinol treatment, normalization of iron kinetics and a moderate decrease in iron storage were demonstrable. The abnormal excretion of uroporphyrin and coproporphyrin were also brought under control. The success of treatment is attributed to the inhibitory effect of allopurinol on xanthine oxidase.