Disulfide reduction in therapeutic monoclonal antibodies can occur during cell harvest operations as a result of cell breakage. Understanding these product quality changes and manufacturers’ ability to control them would likely be of concern to regulatory bodies. To study the biological impact of disulfide reduction, mAbs, including IgG2κ, IgG2λ, IgG1κ, and IgG1λ forms, were partially reduced with dithiothreitol (DTT). Samples generated had approximately 10% or 50% intact molecules as determined by nrCE-SDS. Similar to the type of partial reduction obtained during uncontrolled harvest operations, DTT reduced antibodies were free from sulfur-linked adduct, such as attached cysteine. These partially reduced materials were incubated under physiological (blood-mimicking) redox conditions in vitro to follow the fate of the interchain cysteines. Within 8 h, the original disulfide bonds reformed. For mAbA, an IgG2κ, the initial re-oxidized state favored the IgG2-A disulfide isoform, which then underwent conversion over time to other isoforms. Reduced material was fully active. Results suggest that the type of disulfide reduction would have minimal impact to safety or efficacy. Antibody re-oxidation rates were found to be in the order of IgG2κ < IgG2λ < IgG1κ and IgG1λ, the same order as previously determined reduction rates.