We studied 335 subjects, all drug addicts for the presence of the following serological markers: HIV1 antibody, HBsAg, HBsAb, HBcAb totals. We conclude that subjects HIV1 positive (n. 149) present HBsAb in a significantly lower number (p greater than 0.001) than HIV1 negative subjects (n. 95). The presence of HBcAb isolated is significantly higher (p greater than 0.001) in subjects HIV1 positive. They show an altered serological response to HBV compared to subjects HIV1 negative.