Blood will be drawn from study participants prior to immunization, 1 month after completion of primary immunization and at study exit (week 72 for ATN 024 and week 76 for ATN 025) for cytokine assays and enumeration of antibody-secreting cells. In addition, the antibody to HBV surface antigen will be determined 2 and 4 weeks after supplemental immunization in nonresponders to the primary series and at study exit.