Among relatives of parturients of Majorca island a statistically higher prevalence of HBV markers was found among children (22.8%) and husbands (43.8%) of 49 HBsAg chronic carriers as compared to 2.7% and 19.2%, respectively, among the corresponding relatives of 79 susceptible controls. Prevalence of the carrier state was 0% among both children and husbands of susceptible women, 2.1% (NS) and 11.4% (p less than 0.0001) among husbands and children, respectively, of chronic carrier parturients with a proportion of chronic antigenemia among subjects with HBV markers, that reaches 50% in children and only 4.8% (p less than 0.01) in adults. Following active-passive immunization, an active response of anti-HBs (3.4%), and HBsAg (1.7%), was achieved, after 12 months of follow-up, in 59 newborns of chronic carrier parturients. Detection of HBsAg prior to delivery as well as immunization both of newborns and susceptible household contacts of chronic carrier mothers should become general.