AbstractAs part of an investigation to identify potential new viral reduction strategies, ultraviolet‐C (UV‐C) light was examined. Although this technology has been known for decades to possess excellent virus inactivation capabilities, UV‐C light can also introduce significant unwanted damage to proteins. To study the effect on monoclonal antibodies, three different antibodies were subjected to varying levels of UV‐C light using a novel dosing device from Bayer Technology Services GmbH. The range of fluencies (or doses) covered was between 0 and 300 J/m2 at a wavelength of 254 nm. Product quality data generated from the processed pools showed only minimal damage done to the antibodies. Aggregate formation was low for two of the three antibodies tested. Acidic and basic variants increased for all three antibodies, with the basic species increasing more than the acidic species. Peptide maps made for the three sets of pools showed no damage to two of the three antibody backbones, whereas the third antibody had very low levels of methionine oxidation evident. Samples held at 2–8°C for 33 days showed no increase in aggregates or charge variants, indicating that the proteins did not degrade and were not damaged further by reactive or catalytic species that may have been created on exposure to UV‐C light. Overall, UV‐C light was shown to induce very little damage to monoclonal antibodies at lower fluencies and appears to be a viable option for viral inactivation in biotechnology applications. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009