For many years a test in chicks or guinea pigs has been specified in the Ph. Eur.(2) as the assay for IPV (Poliomyelitis vaccine (inactivated), 1999:0214). However, a WHO collaborative study of immunogenicity assays of IPV found that these tests are poorly standardised (Wood and Heath 1995). An alternative test in rats (van Steenis et al. 1981, Bevilacqua et al. 1996) was found to be less variable than the test in chicks or guinea pigs. After an international consultation, the Ph. Eur. Commission, through the Biological Standardisation Programme of the EDQM, initiated a project to evaluate a rat in vivo bioassay. This study was performed under the aegis of the Biological Standardisation Programme and supported by the Council of Europe and the European Commission.