Following infection with hepatitis B virus (HBV), the period before symptomatic disease is now recognized as a time of dynamic interaction between virus and host. Recent work has shown that this period is the phase of infection during which maximal changes in virus replication and the activation of critical components of the immune system occurs. This suggests that the different outcomes following exposure might be determined during the early phase of infection, before the onset of clinical disease. The hypothesis that small differences in the dynamic relationship between host and virus, such as in the kinetics of HBV replication, may influence the final outcome of infection, will be discussed.