The primary objective is to evaluate the safety and efficacy of eculizumab in transfusion dependent patients with hemolytic PNH.

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