The formation of protein aggregates is a particular concern for parenteral administration biopharmaceuticals due to increased immunogenicity. As a consequence, there is an expectation from regulatory agencies for companies to monitor levels of subvisible particles present in therapeutic protein products initially and over the course of the shelf life. Increasingly, interest has focused on subvisible particles between 0.1 – 10 µm, a size range that has, up to recently, been challenging to study. The development of Resonant Mass Measurement technology in the Archimedes system provides a unique solution to this challenge, delivering quantitative data for particles between 0.2 - 5 µm as well as the ability to distinguish between negatively buoyant particles, such as protein aggregates, and positively buoyant particles such as silicone oil. This webinar will provide an overview of the current techniques available for studying subvisible particles, and demonstrate the unique abilities of the Archimedes system in characterizing and quantifying particles in a size range that has, up to now, been a challenge to the biopharmaceutical industry.