After the 1988 World Health Assembly resolution to eradicate poliomyelitis, the Global Laboratory Network for Poliomyelitis Eradication (the laboratory network) was established by the World Health Organization (WHO). The laboratory network is one component of an international surveillance system for detecting polioviruses through laboratory investigation of stool samples from persons with acute flaccid paralysis (AFP). This infrastructure is critical for guiding strategies to eradicate polio globally. This report summarizes the laboratory network's performance and describes the location and characterization of wild poliovirus (WPV) and vaccine-derived poliovirus (VDPV) during January 2002-June 2003. The achievement and maintenance of polio eradication globally requires the continued support of national governments and partner agencies.