In Tari, Southern Highlands Province (SHP), Papua New Guinea (PNG), pneumococcal polysaccharide (Pne PS) vaccine was offered to women at 28-38 weeks gestation. Blood samples were collected for measurement of pneumococcal antibody titres prior to immunization, from mother and cord at delivery and from their children at ages 1-3 and 4-6 months; samples were also collected in a subset of children before and 1 month after Pnc PS vaccine was given at age 8-9 months. Serum was collected from unimmunized women and their children at delivery and from children of unimmunized women at the same ages in infancy. There were no differences in neonatal or post-neonatal mortality rates or congenital abnormalities in the children of 235 immunized and 202 unimmunized women. There was a significant increase in antibody titres to pneumococcal serotypes 5, 14 and 23F in immunized women but not for serotype 7F. Geometric mean titres (GMTs) of antibodies for serotypes 5 and 23F were significantly higher in children of immunized women than in the unimmunized group up to age 2 months and for serotype 14 significantly higher to age 4 months. Maternal immunization did not significantly affect the children's capacity to make antibody responses to immunization with Pnc PS vaccine in infancy. The findings of this study and those in several other developing countries provide support for the concept of Pnc PS maternal immunization and justify the planning of large-scale efficacy trials. (C) 2002 Elsevier Science Ltd. All rights reserved.