In order to determine the frequency of HBAg in Campania, the AA. have examined a large number of liver patients accurately selected and subdivided in five classes: acute hepatitis, chronic hepatitis, cirrhosis, hepatocarcinoma, and various liver diseases. They have employed radioimmuno assays (RIA) with human and guinea pig antibodies and techniques of passive haemoagglutination. The percentage of HBAg positive subjects among the various classes of liver diseases determined with these techniques is significantly higher than the one remarked by the AA. in 1972 by electrosineresis on the same population. Both RIA and haemoagglutination supply satisfactory results, although for haemoagglutination one must remember the subjectiveness of the reading.