The HBsAg status and demographic data of 2480 pregnant women who attended antenatal clinics at Maternal and Child Health Centres in Hong Kong were collected by means of a self-administered questionnaire over a 1-week period in July 1996, to explore the underlying reason of a higher than expected HBsAg prevalence. Local women constituted 49·2% of the sample, mainland Chinese 39·7% and others 11·1%. The overall HBsAg prevalence was 10·0%. When related to place of birth, those born in Hong Kong had a prevalence of 8·4% whereas the prevalence of those born in mainland China was 13·1% (P<0·001). The overall HBsAg carriage rate is high because of a higher rate in immigrants in the community. It is apparent that the HBsAg prevalence of local people in Hong Kong has been decreasing in the past decade. Overall, the current HBsAg carriage rate in the local adult population is estimated to have declined to about 8%.