The immune responses to hepatitis B vaccine were studied in 11 hepatitis B surface antigen (HBsAg) carrier children who had cleared HBsAg but failed to develop hepatitis B surface antigen antibodies (anti-HBs) in sera (group 1), 5 HBsAg carrier children who had cleared HBsAg and developed detectable anti-HBs in sera (group 2), and 5 healthy subjects seronegative for all hepatitis B virus (HBV) markers (group 3). After receiving three doses of HB vaccine, group 1 subjects failed to develop detectable anti-HBs. Subsequently, each subject of the three groups was given one dose of the same vaccine for a cellular immunity study, and a measurable proliferation of peripheral blood mononuclear cells (PBMC) to HBsAg was detected in 1 of 8 (12.5%), 0 of 5, and 4 of 5 (80%) of the cases in each group, respectively, after vaccination. The removal of CD8+ cells enhanced the HBsAg blastogenic response in group 3 but did not reverse the unresponsiveness in group 1 and group 2 subjects. The addition of interleukin (IL)-2 in culture reversed unresponsiveness in all cases except one case in group 1. Compared with before vaccination, PBMC from group 2 subjects produced significantly less interferon gamma (IFN-gamma) and more IL-4 in response to HBsAg after vaccination, a cytokine response not observed in group 1 subjects. HLA typing indicated that 3 of 10 patients in group 1 (30%) and 1 of 5 patients in group 2 (20%) had HLA-DRw14-DRw52, a marker previously linked to low anti-HBs response to hepatitis B vaccine in Taiwan. We conclude that the underlying causes of poor anti-HBs response in group 1 subjects are multifactorial, including specific failure of antigen presentation or T-cell activation, or the lack of T helper (Th)2 cell-like response to HBsAg. HLA-DRw14-DRw52 does not confer absolute nonresponsiveness to HBsAg. These patients are not benefited by hepatitis B immunization.