The age-prevalence of antibodies directed against the hepatitis viruses A (anti-HAV) and B (anti-HBs and anti-HBc) has been studied in an open sample of population of Turin (Italy), made up by 680 persons. Is has been shown that all three types of antibodies are present at birth, thast they progressively decrease and than again raise, from 6-10 years of age, up to 70-75%, 35% and about 40% in adults, respectively for anti-HAV, anti-HBs and anti-HBc. A further peak over 97% after 40 years for anti-HAV likely means a past higher spreading of the virus. The conclusion is drawn that, for both hepatitis A and B, the percentage of positive and the time of appearance of active humoral immunity after the loss of maternal antibodies are typical medium level of hygienic conditions. The comparison of anti-HBs and anti-HBc behaviour has shown that the latter is more frequent and at least as persistent as the former, and that it should not therefore be obligatory considered ia a marker of viral replication.