Asparagine-linked glycosylation of the constant region of monoclonal antibodies (mAbs) plays an important role in their stability and efficacy and is a critical product quality attribute that needs to be consistent between various process changes and production lots. Exact product quality match is also of the utmost importance for the development of biosimilar protein therapeutics. This poses a process development challenge since mAb glycosylation profiles can fluctuate easily with changes in process parameters. Therefore, there is a need to identify methods to modulate glycosylation levels on therapeutic antibodies during a production run in order to maintain consistent product quality profiles between different drug lots. Here, we demonstrate the use of a small molecule ionophore, monensin, to increase high mannose levels on multiple therapeutic human immunoglobulins (IgGs) in both plate-based small scale production models as well as in production bioreactors. This method is simple to implement and readily applicable for multiple production cell lines. Moreover, high mannose levels can be increased without significant negative impact on titer or cell culture performance. As such, monensin gives us a manipulable product quality lever. Biotechnol. Bioeng. 2015;112: 1383-1394. (c) 2015 Wiley Periodicals, Inc.