Under the provisions of the Workplace Hazardous Materials Information System, workers in Canada must be provided with accurate and comprehensive Material Safety Data Sheets (MSDSs) describing controlled products used in the workplace. As part of an ongoing auditing project, the MSDSs of some controlled products in use under federal jurisdiction were assessed for accuracy and completeness of their ingredient disclosures. Chemical analyses of samples using gas chromatography-mass spectrometry, infrared spectrophotometry, X-ray fluorescence, and wet methods, were performed to verify the ingredient disclosures in accompanying MSDSs. In this article, analytical processes and results are presented for three cases in which MSDS ingredient disclosures were incomplete. The products included a synthetic lubricant used in a mining operation, a detergent concentrate used for aircraft cleaning, and an epoxy reducer used in aircraft maintenance. In each case, undisclosed hazardous ingredients were detected at concentrations which required their disclosure. In at least one of these cases, the information provided in other sections of the MSDS failed to adequately describe the hazards and required protective measures for the composition discovered. Because the results suggest circumstances in which the inaccurate MSDS could act as a mechanism for workplace injury, compliance measures including employer, inspector, and user education, improved MSDS writer qualifications, and the incorporation of chemical analysis in active auditing programs are recommended.