The goal of this study is to evaluate the clinical effectiveness of the rituximab at the adults with a chronic immune thrombocytopenic purpura (>=6 months of evolution) and severe (platelets <= 30x109/L) and candidate to a splenectomy. The objective is to obtain after a treatment by the rituximab a satisfactory response to one year, defined by a number of platelets higher than 50x109/L and at least 2 times superior with the persistent initial figure without treatment during one year after the end of the treatment.