Monoclonal antibodies (MAbs) are increasingly formulated at concentrations >100 mg/mL as a means to deliver a high dose in a low volume (1,2). Such high-concentration solutions are commonly opalescent (3,4), an undesirable characteristic of biopharmaceutical products for several reasons. Although it may be only aesthetic, opalescent products are not considered pharmaceutically “elegant.” Of more serious concern, opalescence may be a precursor to aggregation and indicate a propensity toward decreased product stability or quality. The term opalescent refers to…