The active immunisation by means of vaccination is the best strategy against the B hepatitis virus. Hevac B vaccine was administered to sixty one children (30 boys and 31 girls) aged 1 month 14 years co-inhabitants with chronic carries of virus. After administering three dosages, seroconversion, giving protecting titres (greater than or equal to mU/ml) was obtained in 57 children. Levels in three boys and one girl were not protective. Retarded immunity examination showed alterations of T-Lymphocyte subpopulations only in the girl. The four non responders received a supplementary vaccination a month later, beside the booster dose given one year later (T12). Only two boys had no seroconversion. In spite of the four vaccination four children had antibody titers below 100 mU/ml.