Study Using Eculizumab in Transfusion Dependent Paroxysmal Nocturnal Hemoglobinuria (PNH) Patients

Inclusion Criteria: * Must have required at least 4 transfusions in the past 12 months * PNH type III red blood cell (RBC) clone by flow cytometry of \>10% * Lactate dehydrogenase (LDH) level \> 1.5 x upper limit of normal * Platelet count \> 100,000/mm3 * Patient taking erythropoietin must be on a stable dose for at least 26 weeks * Patient taking immunosuppressants must be on a stable dose for at least 26 weeks * Patient taking corticosteroids must be on a stable dose for at least 4 weeks * Patient taking coumadin must be at a stable INR for at least 4 weeks * Patient taking iron supplements or folic acid must be on a stable dose for 4 weeks * Willing and able to give written informed consent * Must avoid conception Exclusion Criteria: * Mean hemoglobin level prior to transfusion over the previous 12 months is \>10.5 gm/dl * Absolute neutrophil count \<500/ul * Active bacterial infection * Hereditary complement deficiency * Participation in any other investigational drug trial or exposure to other investigational agent, device, or procedures within 30 days * Pregnant, breast-feeding, or intending to conceive * History of meningococcal disease * History of bone marrow transplantation