 The presence of a specific mutation in the gene known as B-RAF has been found in patients who have Hairy Cell Leukemia. In this study this specific mutation known as V600E will be ascertained in peripheral blood samples of patients who have this disease and in a group of patients who have a similar chronic lymphoproliferative conditions such as splenic marginal lymphoma. The finding of this specific mutation will help to verify or exclude the diagnosis of Hairy Cell Leukemia and determine whether patients are in remission. 