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

Inclusion Criteria:

• PNH > 6 months
• Type III PNH red blood cell (RBC) clone by flow cytometry >10%
• At least one transfusion in the past 2 years but no more than 3 transfusions in the past 12 months; or personal beliefs that preclude the use of transfusion with severe hemolytic PNH
• Lactate dehydrogenase (LDH) >1.5 x upper limit of normal
• Must avoid conception
• Willing and able to give written informed consent

Exclusion Criteria:

• Platelet count of <30,000/mm3
• Absolute neutrophil count <500/ul
• Active bacterial infection
• Hereditary complement deficiency
• History of bone marrow transplantation
• Participation in any other investigational drug trial or exposure to other investigational agent, device or procedure within 30 days
• Pregnant, breast-feeding, or intending to conceive
• History of meningococcal disease