1. The use of interferon in hepatitis B will bring about a favourable course of the disease, which is reflected in a normalisation of liver function tests. 2. The concentration of surface antigens is distinctly reduced, with a lower titre remaining for a longer period of time. 3. The level of the dosage chosen seems to be optimal. However, treatment has to be continued for a period of several months, probably for about 1 year. 4. In childhood the side-effects of interferon are minimal, they are restricted to febrile reactions. 5. In our investigations no sure hematological deviations could be identified in the treatment with interferon. 6. The study must be complemented by analysing further antigens, such as E antigen, allowing the course of disease to be characterised more distinctly. 7. In order to give a final assessment of the therapy the observation of patients must be continued after terminating the treatment, the histological improvement in the further course having to be confirmed by liver biopsies.