Evaluation of the Long-term Hepatitis A and B Antibody Persistence in Healthy Adult Subjects, Primed 16 to 20 Years Earlier With GSK Biologicals' Combined Hepatitis A and B Vaccine, Twinrix® (SB208127) in Study HAB-084 (208127/084)

Inclusion Criteria: * Subjects who, in the opinion of the investigator, can and will comply with the requirements of the protocol. * A male or female who received two/three doses of Twinrix according to his/her group allocation in study HAB-084 (208127/084), and received no further dose of any hepatitis A and/or B vaccine since then. * Written informed consent obtained from the subject. Exclusion Criteria: * Chronic administration (defined as more than 14 days in total) of immunosuppressants or other immune-modifying drugs within six months prior to study entry. Inhaled and topical steroids are allowed. * Administration of long-acting immune-modifying drugs within six months prior to the study entry. * Concurrently participating in another clinical study, at any time during the study period, in which the subject has been or will be exposed to an investigational or a non-investigational vaccine/product (pharmaceutical product or device). * Administration of any hepatitis A and/or B vaccine at any time since completion of the primary vaccination series in HAB-084 (208127/084) study, including a challenge dose of the study vaccine, as a part of the study procedures, during the long-term persistence phase. * Documented history of hepatitis A or B disease since completion of the primary vaccination series in HAB-084 (208127/084) study. * Any confirmed or suspected immunosuppressive or immunodeficient condition, based on medical history and physical examination (no laboratory testing required). * Administration of immunoglobulins within six months prior to study entry.