Both the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) have developed regulatory guidelines on biosimilars (1, 2). These comprehensive documents provide clear guidance on what the agencies expect from structural characterization studies. Using state-of- the-art instrumentation and techniques is expected, but the use of orthogonal techniques in structural comparability assessments is also required. The application of orthogonal analytical techniques will provide a firm structural foundation to claims of biosimilarity. Characterization methods verifying and supporting conclusions drawn…