109 biopsy samples from 35 HBAg serologically positive and 74 negative patients were examined by IFL for the presence of the surface and core antigenic determinants associated with the Dane particle. In no serologically negative case was specific IFL detected. Different patterns were observed in serologically positive patients: negative in acute hepatitis, strongly positive cytoplasmic HBs fluorescence in chronic HBAg carriers with normal liver, and discrete HBsAg parenchymal and mesenchymal staining and variable HBcAg staining in chronic liver disease, with HBsAg appearing more frequently in active and HBcAg in active disease. These results are compared with recent reports in this field and the clinical significance of the intrahepatic localization of HBAg is discussed.