Close family contacts of hepatitis B virus (HBV)-related chronic liver disease patients have a high risk of exposure to HBV. Variable responses to vaccination have been reported in family contacts, especially in previously exposed contacts (IgG antiHBc-positive). Seventy-nine healthy family contacts, who were HBsAg-negative with normal alanine amino-transferase level and no evidence of liver disease, were vaccinated using a recombinant HBV vaccine, irrespective of past exposure status. A significantly higher number of previously exposed subjects (n = 25; Group I) developed early seroprotective anti-HBs titers with 2 initial doses of vaccine compared to the unexposed contacts (Group II; n = 54) (64% vs. 33%, respectively; P < 0.05). However, the responses were comparable on completion of the schedule (96% vs. 94%, respectively). HBV DNA was detected in 11 of 25 (44%) exposed and none of the unexposed contacts at baseline. Post-vaccination, 3 of 11 (27%) subjects became HBV DNA-negative and remained negative for the next 12 months. These results suggest that exposed family contacts achieve efficient seroprotection after HBV vaccination, irrespective of the IgG anti-HBc status. The response to vaccination resembles an anamnestic reaction and possibly demonstrates a therapeutic effect.