185 asymptomatic heroin addicts in whom the incidence of positivity as for HBsAg was 9.1%, were examined. From the anamnesis, these carriers has a higher frequency of icteric events in comparison with patient controls, while they did not show differences in distribution according to age, duration of the toxicomania and regional origin of the family. 38 heroin addicts were alcoholics too: 6/38 were HBs carriers, whereas 11/147 non alcoholic were carriers. The group of HBsAg positive addicts showed an analogous alteration of the transaminase levels as regards the patient controls, while the incidence of hypoalbuminemia and hypergammaglobulinemia was higher. In consideration of these results, the possible responsibility of toxic factors (alcohol) and alterations of the immune reactivity as to the prolonged permanence of HBsAg in circle is discussed.