The current tests for inactivated poliovirus vaccine (IPV) potency need standardization between laboratories. A collaborative study has been initiated to assess the suitability of candidate reference materials, assess the suitability of different ELISA methods for D determination, and to assess the variability of a standard ELISA method in different laboratories, using the same reagents and coded samples. The materials included in this study are two commercially prepared candidate reference materials; the primary reference PU78-02 currently used by several laboratories, vaccines from different manufacturers shown to be immunogenic in humans; IPV produced from Sabin strains and vaccines of poor in vivo potency. The study will be divided into two phases. The first phase which has been completed, looked at in vitro assays (the second phase will look at in vivo assays). An ELISA developed at CBER using as detection antibodies monoclonal antibodies specific for D antigen is the candidate standard method. We filled and lyophilized our in-house reagents for distribution to collaborators. Several tests were performed to validate the lyophilized reagents prior to mailing. We prepared a detailed SOP which included the dilution schemes for both practice antigens and test antigens. The collaborators have received an ELISA kit containing plates, polyclonal and monoclonal antibodies and monotypic antigen of all three poliovirus types for practice together with the SOPs and the results of our tests using the monotypic antigens. The test antigens labeled A-F were mailed at a later date. Test results have been compiled in a draft form and are being evaluated. We plan to propose using Balb/c mice as a candidate standard in vivo potency method for the second phase of this collaborative study. We will be involved in the analysis and reporting of the study at each phase.