This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Porphyria cutanea tarda (PCT) is the most common human porphyria and the most responsive to treatment. Two very different approaches to therapy are considered effective. Repeated phlebotomy is most widely used, but has disadvantages that include discomfort, inconvenience and expense. We hypothesize that a low-dose regimen of the 4-aminoquinoline antimalarial drugs, either hydroxychloroquine or chloroquine, is more convenient and cost-effective but is not widely used as first line therapy. A randomized study with frequent and detailed assessment of efficacy is proposed to compare these treatments. Eighty patients with well-documented PCT will be enrolled in this prospective, randomized, unblinded phase 2-3 noninferiority study comparing treatment by phlebotomy with treatment by low-dose hydroxychloroquine. Patients are characterized in terms of known risk factors for PCT, including ethanol use, smoking, hepatitis C, HIV infection, estrogen use, HFE mutations and autosomal dominant inheritance of a partial deficiency of uroporphyrinogen decarboxylase(UROD) due to UROD mutations (as in familial PCT). Plasma and urine porphyrin concentrations will be measured at 2-week intervals for 6 months. It is likely that this study will justify more general use of low-dose hydroxychloroquine and eventually lead to treatment of PCT as an approved indication. Greater acceptance of this approach will lower health care costs and increase the convenience of treating PCT.