The best testimony to the vitality and intellectual exuberance of the hepatitis scientific community comes at the end of each triennal symposium, when the balance is drawn between what was achieved and what still needs to be learned. It then invariably happens that despite several days of exchanges of an incredible mass of new information we recognize that a greater scientific workload lays ahead to solve the many questions raised during the symposium. The Tokyo meeting is no exception; if anything, it has been more exhaustive and provocative than previous symposia. The understanding of the pathogenic mechanisms of hepatitis B virus (HBV) and hepatitis C virus (HCV) now appears within closer reach, with the recognition of the heterogeneity of HBV and HCV and the implications that such heterogeneity may bear on the variability of human diseases. The truth, however, is likely to be more complex and the case was raised for the critical role of host response to the virus in determining disease.