Streptococcus pneumoniae causes considerable morbidity and mortality in developing nations. The World Health Organization estimates that pneumonia accounts for 5 million childhood deaths each year, 30% of which are caused by S. pneumoniae.1 A total of 84 pneumococcal capsular polysaccharide (PS) serotypes are known2; however, only 7 types (4, 6B, 9V, 14, 18C, 19F and 23F) account for 75% of worldwide childhood disease.3 Recent Colombian data in children showed that types 1, 5, 6A, 6B, 14, 18C, 19F and 23F comprised 86% of the 141 pneumococcal isolates obtained from normally sterile body sites.4 Serum type-specific anti-PS antibody concentrations in infancy are closely related to the concentration of maternal type-specific IgG antibodies and to the infant's anti-PS antibody synthesis.5, 6 Vaccine-induced serum antibodies against each PS confer type-specific immunity in children and adults.7 The anti-PS antibody nadir between 6 and 18 months of age, caused by disappearance of maternal antibody and slow maturation of the anti-PS immune response, accounts for the peak incidence of pneumococcal disease during this period. This information is based on studies in developed countries; little is known about the prevalence of naturally acquired or vaccine-induced anti-PS antibody in children from developing nations. We measured naturally acquired IgG anti-PS antibodies against 10 common pneumococcal capsular polysaccharides in serum from 78 randomly selected, age-stratified, healthy Colombian children. A cohort of age-matched, healthy Minnesota children was studied for comparison.