Neoplastic disorders sometimes accompany a renal transplant. Herein, we report a large granular lymphocyte (LGL) leukemia patient with pure red cell aplasia (PRCA) after renal transplantation. A 36-year-old female was presented to our department with anemia in February 1996. She had undergone hemodialysis because of pregnancy in December 1981. She received a renal transplantation from her mother in April 1986. After the transplantation, she received cyclosporin A (CyA) at 2 mg/kg/day, mizoribine at 1 mg/kg/day, and methylprednisolone at 0.1 mg/kg/day for 8 years. In July 1995, her hemoglobin level dropped to 9.3 g/dl, and anemia developed gradually. In January 1996, her hemoglobin was 5.8 g/dl, and she was given a red blood cell transfusion. Laboratory findings were as follows: RBC 1.46 x 10(12)/L; hemoglobin 5.8 g/dl; hematocrit 17.8%; leucocytes 5.2 x 10(9)/L with 62.4% neutrophils, 34.1% lymphocytes, 2.6% monocytes; platelets 50.8 x 10(10)/L; reticulocytes 0.4%. Bone marrow aspirate smears and biopsy sections revealed normal myeloid and megakaryocyte differentiation with few erythroid precursors. The lymphocytes were of medium size with granules in the cytoplasm. More than 90% of lymphocytes were of the LGL type. Surface markers of peripheral blood mononuclear cells demonstrated increases in the CD2+, CD3+, CD4-, and CD8+ populations. A monoclonal rearrangement of T-cell receptor (TCR)-beta chain gene was found by Southern blot analysis of the mononuclear cells in peripheral blood. A diagnosis of LGL leukemia with PRCA was made. During the next 4 months, she received six red blood cell transfusions, a total of 12 U. In March 1996, the patient was treated with cyclophosphamide (1 mg/kg/day). After 1 month of treatment, serum GPT levels increased to 60 IU/l. The dose of cyclophosphamide was reduced to 0.5 mg/kg/day. Two months after initiation of the therapy, the patient developed reticulocytosis and blood transfusion was not needed thereafter. During remission, the number of CD2+, CD3+, CD4-, and CD8+ lymphocytes decreased. Large granular lymphocytes decreased to less than 10% of peripheral blood. The monoclonal rearrangement of the TCR-beta chain gene in peripheral blood disappeared.