The authors studied 496 patients with chronic persistent or aggressive hepatitis, and active or non-active hepatic cirrhosis, and 396 non-hepatic patients. AgHB was detected in the serum by immuno-electrophoresis and by immuno-diffusion and, in the liver, by needle biopsy, using immuno-fluorescence. The liver diagnosis was made histologically. AgHB was found in 34.2% of patients, more often in chronic active hepatitis (53.7%) than in inactive forms (23.2%). This finding may be interpreted as a sign of severity, chronic aggressive hepatitis is more frequently caused by B virus and by its persistence in the liver. In all cases of chronic, aggressive hepatitis studied with AgHB in the serum, AgHB was detected in the nuclei of the liver parenchyma cells. It should be emphasized that there is no significant difference from the immunological point of view, between patients with AgHB and the others, the levels of gamma-globulin and immunoglobulin were higher in the former. The increased frequency of AgHB in the active forms of the disease compared with stabilised forms, reinforces its physiopathological, diagnostic and prognostic significance.