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

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