From July 1984 to September 1987, 981 women at third trimester of pregnancy were screened for HBsAg. 26 women were identified as being HBsAg carrier. The study of HBV markers and anti-HBV antibodies was conducted on these women and their offspring to evaluate the presence of intrauterine infection, and the newborns response to passive active immunization in relationship to their markers status during pregnancy. HBsAg, HBeAg, anti-HBe and anti-HBc were assayed on the plasma drawn form the mother, on the amniotic fluid drawn by transabdominal amniocentesis and on funicolar blood samples drawn immediately after delivery. IgM anti-HBc were assayed on amniotic and funicolar samples. HBsAg, anti-Hbc and anti-Hbe were present in 42.8%, 100% and 50% of amniotic samples; whereas the percentage of the same markers in funicolar samples were 50% for HBsAg and 100% for anti-HBc and anti-HBe. In no amniotic or funicolar samples were IgM anti-HBc antibodies present. Anti-HBs, anti-HBc and anti-HBe were assayed on the newborns at 2, 16, 12, 18 months to evaluate the response to immunization. Response to passive-active immunization was protective in all newborns independently from their antigenic status during intrauterine life. Anti-HBc antibodies were cleared within 18 months from delivery, while anti-HBs got a protective title within 6 months from delivery, persisting in 88.8% of cases at 18 months.(ABSTRACT TRUNCATED AT 250 WORDS)