The European Pharmacopoeia (Ph. Eur.) hydrolytic resistance method for glass vials is routinely used to screen pharmaceutical glass vial supply. In an effort to better understand and control the factors affecting method precision and robustness, several potential sources of variability in the Ph. Eur. alkalinity method have been studied for 3 cc glass vials. Method parameters including vial rinsing, vial covering, autoclave cycle execution, sample hold times, and titration procedure were evaluated in this study. The results of this study indicate the method parameters which require stringent control in order to achieve acceptable method precision and robustness.LAY ABSTRACT: The European Pharmacopoeia (Ph. Eur.) hydrolytic resistance method for glass vials is routinely used to screen biopharmaceutical glass vial supply. The method was studied to assess contributions to its variability and to potentially improve its reliability. The results of this study indicate which method parameters require stringent control in order to generate reliable data using the Ph. Eur. hydrolytic resistance method.