The first worldwide interlaboratory study on persistent organic pollutants (POPs) under the Stockholm Convention was organized, with a participation of 103 laboratories from Asia, Europe, the Americas, Africa and Australia, of which the majority submitted data on polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). The participating laboratories were requested to analyze different matrices (i.e. two test solutions, and test materials for fish, sediment, fly ash and human milk). All results were statistically evaluated according to the procedures used in the European Union-based QUASIMEME proficiency-testing scheme.