The highest incidence of severe pneumococcal infections in children occurs in the first 6 months of life; however, immunization of infants with the existing polysaccharide vaccines is ineffective. We wished to determine the prevalence of immunoglobulin G (IgG) pneumococcal antibodies in unimmunized Brazilian mothers and their transplacental transmission to term and preterm infants. Total IgG, IgG1 and -2 subclass levels, and IgG antibodies against Streptococcus pneumoniae serotypes 1, 3, 6B, 9V, and 14 were determined in 15 pairs of mothers and term newborns (gestational age, 37 weeks) and in 18 pairs of mothers and preterm newborns (gestational age, 32 to 36 weeks). Serotype-specific anti-pneumococcal antibodies were detected by a recently standardized enzyme-linked immunosorbent assay calibrated with the 89-SF reference serum. Varying percentages of the mothers had antibody concentrations below arbitrarily defined protective levels: 33% for serotype 1, 67% for serotype 3, 30% for serotype 6B, 52% for serotype 9V, and 22% for serotype 14. In term newborns, IgG1 concentrations were slightly higher than maternal concentrations; in preterm newborns, the concentrations were much lower. Concentrations of IgG2 in term and preterm infants were significantly lower than in the mothers. Transplacental transmission of antibodies to serotypes 3 and 14 was clearly different from that of antibodies to serotypes 1, 6B, and 9V. Concentrations of IgG antibodies against serotypes 3 and 14 were similar to or higher than those of the mothers; against serotypes 1, 6B, and 9V they ranged from 77 to 83% of maternal concentrations in term newborns and also in preterm infants, although transplacental transmission of antibodies was proportionally lower for each specific serotype in preterm than in term infants. These data are relevant for developing strategies to protect infants against pneumococcal infections in the first months of life. Our findings and a review of existing information stress the importance of understanding the relationships among pneumococcal immunization, IgG subclass antibodies to individual serotypes, transplacental transport, half-life, and antibody function and their protective values against infection.