Quantitation of specific IgG to polysaccharides (serotypes) of Streptococcus pneumoniae provides the basis for evaluating vaccine efficacy. Different enzyme-linked immunosorbent assay (ELISA) methods are used internationally, making comparisons between laboratories difficult. We undertook an inter-laboratory comparison between two international laboratories performing serotype-specific IgG ELISAs using a panel of well-characterized serum samples: the Murdoch Childrens Research Institute Pneumococcal Laboratory (Melbourne, Australia) and the Vaccine Immunology Laboratory, National Public Health Institute (Helsinki, Finland). While good agreement was found for the inter-laboratory comparison for most serotypes, differences in ELISA methodology influenced specific IgG measurement. Therefore, use of the World Health Organization (WHO)-based ELISA methods for measurement of serotype-specific IgG is reliable, accurate and provides consistent results between international laboratories. � 2009 Elsevier Ltd. All rights reserved.