The chapter discusses the issue of ion suppression in mass spectrometry (MS), a technique widely adopted in clinical laboratories for its specificity, sensitivity, and speed. Ion suppression occurs due to the presence of less volatile compounds that affect droplet formation or evaporation, thereby altering the amount of charged ions reaching the detector. The review covers materials that cause ion suppression, such as salts, ion-pairing agents, endogenous compounds, drugs, metabolites, and proteins. It also outlines experimental protocols to examine ion suppression, including signal recovery studies and postcolumn infusion of the analyte to evaluate prolonged ionization effects. Options for minimizing or correcting ion suppression are presented, such as enhanced specimen cleanup, chromatographic changes, reagent modifications, and effective internal standardization. The importance of performing ion suppression studies using expected physiologic concentrations of analytes is emphasized. The chapter highlights the benefits of MS in reducing sample cleanup and chromatographic separation, but also underscores the need for thorough validation to ensure accurate and precise measurements.The chapter discusses the issue of ion suppression in mass spectrometry (MS), a technique widely adopted in clinical laboratories for its specificity, sensitivity, and speed. Ion suppression occurs due to the presence of less volatile compounds that affect droplet formation or evaporation, thereby altering the amount of charged ions reaching the detector. The review covers materials that cause ion suppression, such as salts, ion-pairing agents, endogenous compounds, drugs, metabolites, and proteins. It also outlines experimental protocols to examine ion suppression, including signal recovery studies and postcolumn infusion of the analyte to evaluate prolonged ionization effects. Options for minimizing or correcting ion suppression are presented, such as enhanced specimen cleanup, chromatographic changes, reagent modifications, and effective internal standardization. The importance of performing ion suppression studies using expected physiologic concentrations of analytes is emphasized. The chapter highlights the benefits of MS in reducing sample cleanup and chromatographic separation, but also underscores the need for thorough validation to ensure accurate and precise measurements.