The Bcl-2 family proteins are important regulators of apoptosis and have been implicated in the occurrence of autoimmune diseases. There have been reports that Bcl-2-positive lymphocytes play important roles in pathogenesis of at least some types of autoimmune diseases, including autoimmune hepatitis. In this study, we examined the role of Bcl-2-positive lymphocytes in the development of primary biliary cirrhosis (PBC). The expression of Bcl-2 in lymphocytes infiltrating into the liver was evaluated from liver biopsy specimens of 25 patients with PBC (stage I/II/III/IV, 11/3/8/3) and 24 controls with chronic hepatitis B (CH-B) or chronic hepatitis C (CH-C). Bcl-2 expression in lymphocytes infiltrating into the liver was investigated by immunohistochemistry using a monoclonal antibody to Bcl-2 with an avidin-biotin complex system. Significant overexpression of Bcl-2 in lymphocytes infiltrating into the liver was observed in the early stage of PBC, especially in areas of destructed bile ducts. Most of Bcl-2-positive cells were CD45RO-positive helper T-cells visualized by the double staining method. These results suggest that Bcl-2-positive helper T-cells may have important roles in the pathogenesis of PBC.