In order to determine whether infection with S. mansoni is related to a higher rate of infection with HBV and/or to a higher probability of HBsAg chronic carriage, a population based survey was carried out in Egypt in which HBV markers were studied in 67 subjects with heavy long-lasting S. mansoni infection. Controls were 67 subjects with no or low grade S. mansoni infection individually matched with the cases for age, sex and village of origin. 41.8% of the cases and 37.3% of controls showed no marker of HBV infection. The prevalence rate of anti-HBc alone was 4.5% in the cases and 7.5% in the controls. For anti-HBs the figures were 53.7% and 55.2% respectively. No cases or controls were positive for HBsAg. These data do not support the hypothesis of an interaction between infection with hepatitis B virus and S. mansoni.