A patient, having a huge hepatic hemangioma, presented with decreases in the number of peripheral lymphocytes and in serum concentrations of γ-globulin and immunoglobulin (Ig) G, and a negative purified protein derivatives skin test, indicating that the patient's immunity was impaired. The plasma concentration of transforming growth factor β1 (TGF-β1), a potent immunosuppressor, in the patient was markedly elevated (113 ng/mL, normal < 5). After the surgical removal of the tumor, the plasma TGF-β1 concentration decreased, and the patient's immunity was restored to normal. Northern blot analysis showed an overexpression of the TGF-β1 gene in the hemangioma tissue, while normal control liver tissue expressed undetectable levels of TGF-β1 messenger RNA. These results suggest that the elevated levels of TGF-β1 in the plasma were derived from the giant hemangioma tissue and may have contributed to the impaired immune function in the patient.