1. Primary biliary cirrhosis is a chronic cholestatic liver disease with an autoimmune aetiology. The classical histopathological lesion, of portal tract biliary epithelial cell damage, is accompanied by a T-cell-rich mononuclear cell infiltrate and upregulation of cell surface markers suggestive of local T-cell activation and cytokine release. This suggests that T-cell mediated mechanisms play an important role in tissue damage in primary biliary cirrhosis. 2. CD4+ T-cells specific for the E2 component of human pyruvate dehydrogenase complex (PDC-E2), a highly conserved enzyme which plays a critical role in intermediate metabolism, are present in the peripheral repertoire of the majority of patients with primary biliary cirrhosis. These cells are almost entirely absent from normal and chronic liver disease control subjects. The observations that peripheral blood PDC-E2-specific cells are most commonly seen in early stage disease, when active bile duct damage is occurring, and that PDC-E2- specific cells can be found in the portal tract infiltrate at times when this damage is occurring, suggest that these autoreactive cells may have a role to play in the aetiology of primary biliary cirrhosis. 3. T-cells specific for the whole PDC and its E1 component are seen in significant numbers of normal control subjects as well as patients with primary biliary cirrhosis. Retention of potentially autoreactive cells in the normal T-cell repertoire has been reported for a number of other autoantigens. 4. T-cell epitopes appear to be widely distributed throughout PDC-E2. This is in contrast to the B-cell epitopes which are highly restricted to the inner lipoyl binding domain of the protein.