As regulators become increasingly stringent in demanding a fuller understanding of whole virus preparations, researchers and manufacturers are looking beyond well-known characterization methodologies. Existing technologies for quantifying and characterizing viral preparations such as infectivity assays, quantitative polymerase chain reaction (qPCR), and protein assays provide crucial information but tell only half the story. We evaluated a unique technology developed by NanoSight Ltd. (www.nanosight.com) for visualizing viruses in liquid suspensions, measuring their approximate concentration, and characterizing their state of aggregation. Information generated…