The HB antigen of the hepatitis B (HB) virus, studied by counter immunoelectrophoresis shows a prevalence of 8.7% in 1,860 rural Malians and 11.3% in 764 blood donors from Bamako. Amongst 1,350 hospitalised patients, no correlation could be established between the HBs antigen chronic carriers state and other infectious diseases, malnutrition or genetic deficiencies. On the other hand, the prevalence of HBs antigen is particularly high in hepatic infections: acute and chronic hepatitis (53.5%), cirrhosis (31.5%) and hepatomas (25.3%). The study of the prevalence of hepatitis B by radioimmunoassay of the HBV seric markers was carried out in: --176 "healthy" town dwellers of which 97.2% were carriers of at least one marker--HBs Ag: 16.5%; anti-HBc alone: 34.1%; anti-HBs: 46.6%--. --30 subjects with cirrhosis--HBs Ag: 66.7%; anti-HBc alone: 10.0%; anti-HBs: 23.3%--. --42 subjects with PHC--HBs Ag: 47.6%; anti-HBc alone: 23.8%; anti-HBs: 28.6%--. The difference in HBs Ag carrier state between patients (cirrhosis and PHC) and controls, cross-matched for sex and age, is highly significative--p = 0,0001--.