The objective of this study is to identify genes that are specifically up or down regulated in chronic viral hepatitis and autoimmune liver disease and then to examine how these expression patterns relate (if at all) to clinical outcome. The expression pattern of thousands of genes should provide extremely powerful statistical tools to distinguish between different pathophysiological states. It is well recognized that neither hepatitis B or hepatitis C is directly cytotoxic, their effect appears to be mediated via an immune response. Similarly in individuals with autoimmune liver disease e.g. primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH) immune mediated mechanisms appear to be the cause of their liver disease although the eliciting antigen(s) remain unknown. The pattern of gene expression can give clues as to both the cause and the pathogenesis of disease. For instance, if a disease is caused by an infection, a specific cytokine response is observed which will be different if this infection is viral or bacterial or parasitic. It is also possible that a certain pattern of response would be elicited if the disease is caused as a response to xenobiotic. In patients with autoimmune liver disease, it is possible that an endogenous and/or an exogenous antigen initiates the disease with a subsequent autoimmune response. Finally, it is also possible that a completely unexpected series of cellular events is responsible for pathogenesis, and the microarray experiments will enable us to discover these processes.