The prevalence of HBsAg and anti-HBs among voluntary blood donors, professional blood donors, INBTS laboratory staff, haemophiliacs and the patients and medical personnel of three haemodialysis centres was compared. The 3.4% incidence of HBsAg found among 168,890 voluntary donors was significantly less than the 8.4% found among 378 professional blood donors. The prevalence of HBsAg was higher in male than in female donors, and also higher in single than in married donors. Prevalence of HBsAg was unrelated to ABO-Rh blood group but was related to age. Anti-HBs was found in 30% of voluntary blood donors, 67% of professional donors, 68% of haemodialysis patients, 39% of haemodialysis staff, 86% of haemophiliacs and in only 4.8% of HBsAg carriers. Subtyping of HBsAg found in 100 voluntary donors showed 65 were ay; 5 ad; 10 ad + ay and 20 were untypable.