The goal of current treatment guidelines for most patients with chronic adult ITP is to maintain platelet levels above 30 x 109/L. The conventional first-line therapy is corticosteroids with or without intravenous immunoglobulins, but many patients relapse when steroids are tapered. Standard therapy then is splenectomy, but patients with refractory ITP who do not respond require further therapy. Unfortunately, immunosuppressive agents or other available treatments typically produce only short-term responses. Because of the lack of medical options after first-line therapy, the target population for this first study of anti-CD20 immunotherapy with hA20 are adult patients with chronic ITP who failed at least one standard ITP therapy (i.e., received at least one standard ITP therapy and now present with platelet levels below 30 x 109/L).