NISTCHO is a recombinant Chinese hamster ovary cell line that has been genetically engineered to produce the monoclonal antibody cNISTmAb. This study investigates the stability of the NISTCHO cell line in long-term culture. Low passage number NISTCHO cells from a working cell bank were used to initiate a shake flask culture that was passaged over many weeks, accounting for approximately 129 cell doublings. Cells taken at two-week intervals during this period were used to inoculate fresh cultures, which were monitored over nine days for viable cell concentration, percent viability, and monoclonal antibody production. Results demonstrate consistency among growth curves over time with comparable peak cell densities and cell viabilities. Importantly, cNISTmAb production remained high, with culture titers remaining stable over the culture period and a high number of cell doublings. These findings demonstrate that the NISTCHO cell line has high stability and a sustained capability of producing cNISTmAb over extended culture periods.