Meningococcal serogroup C (MenC) plain polysaccharide (PS) and conjugate vaccines are primarily evaluated by physicochemical methods to ensure that batches are consistently manufactured. As different assays are employed to quantify the MenC PS content of final formulations and bulk intermediaries, there is a need for an International MenC PS Standard to calibrate internal references used in the different laboratories. Twelve laboratories from nine different countries participated in a collaborative study to assess the suitability and determine the MenC PS content of a candidate International Standard MenC PS preparation (08/214). On the basis of the results from this study, it is recommended that the candidate standard 08/214 is established as an International Standard for the quantification of MenC PS content in vaccines and components. It has a content of 1.192 0.192 mg MenC PS/ampoule (expanded uncertainty with coverage factor of k=2.365 corresponding to a 95% level of confidence), as determined by the resorcinol assays carried out by eight of the participating laboratories.