The Hematology Service provides hematology consultations for patients at the Clinical Center and participates in the training of hematology fellows. Patients with a broad range of hematologic disorders must be available in order for the senior staff of the Service to maintain clinical expertise and to provide the breadth of experience necessary for the fellowship program. The purpose of this protocol is to meet these needs by allowing the Hematology Service to see patients with a spectrum of hematologic diseases not studied on existing research protocols at the NIH. These patients will be evaluated over the course of several outpatient visits and returned to the care of their referring physicians.