A modified trichrome stain is described for the intrahepatic localization of the hepatitis B surface antigen; HBsAg containing cells exhibit specific green metachromasia contrasting with the granular brown colour of non infected hepatocytes and with the deep eosinophilic colour of ground glass cells of HBsAg-negative alcoholic or drug hepatitis. The technique is simple and reliable for routine screening of HBsAg positive material; its sensitivity is greater than H & E, similar orcein and inferior to immunohistochemistry as performed on frozen sections. Histological diagnosis can be made on the same slide, since several other morphological details are provided in the trichrome stained preparations. With this technique 387 biopsies from HBsAg seronegative individuals were negative; full cytoplasms metachromasia was mostly seen in asymptomatic HBsAg carriers, focal or partial staining in patients with histological evidence of liver cell necrosis. The presence and the staining pattern of HBsAg were of no help in predicting transition to chronicity or a transition from chronic persistent to chronic active hepatitis.