Among families of blood donors from Languedoc, found to be chronic carriers of HBs antigens, the masculinity ratio of the siblings (number of boys compared to number of girls) calculated on 303 individuals is significantly higher (1,32) than that of the general population (1,05). This rise is still increased when considering only the families where the viral infection is present in the mother (1,73), whereas it is very low when in the father (1,09).