To assess the hepatitis B virus infection risk to household contacts exposed to HBsAg-positive chronic carriers, 169 family members of 20 healthy carriers of HBsAg and of 12 with chronic hepatitis were followed up prospectively for two to five years. All family members are investigated for the presence of serum HBsAg/antiHBs system and for the presence of liver disease. Our results indicate that the family contacts of HBsAg carriers with evidence of chronic liver disease are at greater risk of exposure to HBV than the contacts of healthy carriers and that acquisition of HBsAg is more common among males than among females. Evidence of exposure to HBsAg is very frequent in young age with a striking rise between 10 and 20 years. On the contrary acquisition of anti-HBsAg is more common after 40 years of age. These data suggest that persistent circulation of HBV in a family of chronic HBsAg carrier increases the risk of infection in household contacts and that HBV is eliminated in a more infective form from the carriers with chronic liver disease.