175 Chronic HBs Ag carriers have been discovered in the blood donors of the Calvados blood transfusion center from 1971 to 1979. 72 of them (41%) gave their consent for a clinical and biological study at the end of 1979, after receiving a convocation letter. This work had two aims: - to study the epidemiological factors in this population. - to evaluate the clinical and biological consequences of persistent antigenemia. 1. Epidemiological Study. Most results agree with the literature (higher prevalence in male, age, stay in endemic countries) but some results disagree for several reasons: our donors are all volunteers, HBs Ag prevalence is low in our region, most of the patients are caucasian and with life conditions and habits which may explain some particularities in contagion. Furthermore, the relative number of blood donors found every year as chronic HBs Ag carriers, does not increase in our country. 2. The Clinical and Biological follow-up of 62 HBs Ag carriers (alcoholics excluded) was carried out for 4,3 years on average. No patients developed clinical and biological features of chronic liver disease. After a mean term follow-up, we conclude that the asymptomatic HBs Ag carriers state seems not to be of bad prognostic. Since long term complications cannot be excluded, the follow-up of these patients must be maintained.