A Study to Characterise Immune Responses Following Immunisations With "Fendrix" or "Engerix B" Hepatitis B Vaccines

Inclusion Criteria: 1. Healthy male subjects aged 18-55 years inclusive 2. The subject is, in the opinion of the investigator, healthy on the basis of a physical examination, medical history, blood results, vital signs, with no active disease process that could interfere with the study endpoints. 3. The subject is able to read and understand the Informed Consent Form (ICF), and understand study procedures. 4. The subject has signed the ICF. 5. The subject has not previously received a vaccine for Hepatitis B or contracted Hepatitis B infection. 6. The subject is seronegative to Hepatitis B as confirmed at screening by assessments of sAb, sAg, and cAb. 7. Seronegative for HIV 1 \& 2 antibodies and hepatitis C antibodies at screening. 8. Available for follow-up for the duration of the study. 9. Agree to abstain from donating blood during and for three months after the end of their participation in the study, or longer if necessary. 10. Visa long enough allowing them to complete the study (if applicable). 11. The subject has venous access sufficient to allow blood sampling as per the protocol. Exclusion Criteria: 1. Known hypersensitivity to any component of the vaccines (excipients: sodium chloride, disodium phosphate dehydrate, sodium dihydrogen phosphate; adjuvants: aluminium phosphate, AS04C, aluminium hydroxide; Hepatitis B antigen produced in yeast cells) or subjects who have exhibited hypersensitivity to any other Hepatitis B vaccine, or a history of any allergy that in the opinion of the investigator would contraindicate subject participation. 2. Presence of primary or acquired immunodeficiency states with a total lymphocyte count less than 1,200 per mm3 or presenting other evidence of lack of cellular immune competence e.g. leukaemias, lymphomas, blood dyscrasias, or patients receiving immunosuppressive therapy (including regular use of oral, inhaled, topical or parenteral corticosteroids). 3. Use of any immune suppressing or immunomodulating drugs within 6 months of Visit 1 (screening). 4. Regular use of non-steroidal anti-inflammatory drugs (by any route of administration including topical) within 6 months of Visit 1 (screening) considered by the study physician as likely to interfere with immune responses. 5. Receipt of a vaccine within 30 days of visit 2. Other vaccines (e.g. for travel) may be administered between visit 13 and 14 only. 6. Currently participating in another clinical study with an investigational or non-investigational drug or device, or has participated in a clinical study within the 3 months preceding Visit 1. 7. Any condition that, in the investigator's opinion, compromises the subject's ability to meet protocol requirements or to complete the study. 8. Receipt of blood products or immunoglobin, or blood donation, within 3 months of screening. 9. Unable to read and speak English to a fluency level adequate for the full comprehension of procedures required in participation and consent.