In recent years group B Streptococcus (GBS) has been recognized as a major perinatal pathogen. As with other encapsulated bacteria, protective immunity appears to correlate with serum antibody specific for the homologous capsular polysaccharide antigen of each serotype. Since susceptibility of the young infant to disseminated GBS infection relates to type-specific antibody deficiency in maternal serum, immunization of women with purified GBS type-specific polysaccharides has been proposed as a method for the prevention of infant disease through placental transport of protective antibodies. Candidate native polysaccharides from GBS have been purified, immunochemically and structurally characterized, and employed as immunogen in healthy adult volunteers. Native type Ia, II, and III polysaccharides have been shown to be nontoxic, safe, and immunogenic in approximately 65%, 95%, and 70%, respectively, of nonimmune adults. Antibody response to immunization approaches 100% in previously immune volunteers. Vaccine-induced type-specific antibodies to these candidate polysaccharide vaccines promote in vitro opsonophagocytosis, protect animals given a lethal challenge of homologous organisms, and are predominantly of the IgG isotype. Once similar results can be documented in women immunized during the last half of pregnancy, efficacy of these candidate GBS polysaccharide vaccines in the prevention of neonatal and young infant GBS disease should be evaluated.