BACKGROUND: Protein profiling by surface enhanced laser desorption ionization-time of flight-mass spectrometry (SELDI-TOF-MS) is gaining importance as a diagnostic tool for a whole range of diseases. This report describes a QC procedure, which acts prospectively by checking the calibration before starting profiling experiments. METHODS: A well-defined protocol for calibration of the Protein Biosystem IIc instrument was established, using a commercial QC sample containing independent certified standards and by determination of acceptance criteria. Instrument calibration was performed externally every week with the standards provided by the manufacturer. QC was performed for the period of 5 months. RESULTS: According to the acceptance criteria defined in this study, data points should be in the established range of the process mean+/-2 standard deviations for the mass-to-charge ratios (m/z values), peak intensities, signal-to-noise ratios (S/N), and peak resolutions for insulin and apomyoglobin in the QC sample. Moreover, it was demonstrated that the pipetting variability in the handling of the QC sample significantly contributed to systematic errors and that spotting of a larger volume of QC sample resulted in a better reproducibility. CONCLUSIONS: Stringent quality control of the calibration part of SELDI-TOF-MS experiments prevents unreliable data acquisition from the very start.