Patients must be greater than or equal to 18 years of age.

Peripheral blood absolute LGL count of greater than or equal to 300/ul (performed on a manual differential), with LGL cells having the characteristic appearance of large lymphocytes with abundant pale blue cytoplasm, with or without a perinuclear clear zone, with varying degrees of azurophilic granules.

Immunophenotypic studies of peripheral blood showing an increased population of T-LGL (Staining for: CD3, CD8, and either CD16 or CD57+/- CD56).

Severe neutropenia (less than or equal to 500 neutrophils/uL of peripheral blood), or severe thrombocytopenia (less than or equal to 20,000 platelets/uL, or moderate thrombocytopenia (less than or equal to 50,000 platelets/uL with active bleeding , or anemia (hemoglobin less than or equal to 9 gm/dL), or red blood cell transfusion requirement of greater than or equal to 2 units/month for two months prior to initiation of CsA treatment.

Patients must not have had previous treatment with CsA or FK506.

Patients must not have a reactive LGL lymphocytosis to a viral infection.

Patients must not have a ECOG performance status of greater than 3.

Patients must not be currently pregnant, or unwilling to take oral contraceptives unless postmenopausal.

Mothers must not be breast feeding.

Patients must be able to give informed consent.

Patients must not be HIV positive.