Antibody response to Campylobacter pylori was measured in ethnic groups of Vietnamese, El Salvadorean and Ethiopian origin. The results were compared with the previously reported antibody titres found in sera of culture positive and culture negative patients, patients suffering from duodenal ulcer, white Australian blood donors and Australian Aboriginals. While in Vietnamese the prevalence of serologically positive sera was found to be similar to the white Australian population, numbers of serologically positive sera in El Salvadorean and Ethiopian ethnic groups was found to be very high. The high incidence of serologically positive sera in the Ethiopians correlated with the reported high incidence of duodenal ulcer in this population.