BACKGROUND: In adults, a high prevalence of antibody to the cytotoxin-associated antigen (CagA) of Helicobacter pylori has been linked to the development of more serious gastroduodenal disease. Few investigators have examined this association in children. The purpose of this study was to investigate the seroprevalence of antibody to the CagA antigen as well as other specific H. pylori antigens in children. METHODS: By use of an immunoblot analysis kit, the immune response to specific H. pylori antigens in serum collected from 21 H. pylori-positive symptomatic Australian children, 5 with peptic ulcer disease and 16 with nonulcer dyspepsia, and 33 H. pylori-positive asymptomatic Chinese children. Sera from 20 H. pylori-negative symptomatic Australian children were used as control subjects. RESULTS: Antibody responses to the 26.5-kDa, 30-kDa, and 116-kDa (CagA) antigens were found to be the most prevalent, with 81.5%, 79.6%, and 76% of children, respectively, mounting a response. In contrast, antibody responses to the 19.5-kDa, 35-kDa, 45-kDa, 60-kDa, 89 kDa (VacA), and 180-kDa antigens occurred in 55.5%, 24%, 16.7%, 63%, 37%, and 7.4% of children, respectively. A higher prevalence of antibody response to CagA was found in the symptomatic Australian children with peptic ulcer disease (100%) compared with prevalence in those with nonulcer dyspepsia (56.3%), but the difference did not reach statistical significance. No significant difference was found between the prevalence of antibody to CagA in the Australian peptic ulcer disease group (100%) and that in the asymptomatic Chinese children (81.8%). CONCLUSION: These results suggest that in children CagA is not a marker of specific disease development.