Résumé : A set of CMS MicroStrip Gas Chambers (MSGC) was exposed to a high-intensity 3 GeV/c pion beam at a CERN PS facility for a period of two weeks. The performance of the detectors is reported in terms of stability of efficiency and response to minimum ionising particles as well as to more heavily ionising fragments generated by nuclear interactions. © 1998 Elsevier Science B.V. All rights reserved.