|Recent studies have implicated a role for the liver-secreted glycoprotein fetuin-A in insulin resistance. Fetuin-A negatively regulates insulin action by interacting with the activated insulin receptor and inhibiting insulin-stimulated insulin receptor autophosphorylation and tyrosine kinase activity. This study examined Ser312-fetuin-A phosphorylation status in diet-induced obese (DIO) C57Bl6 mice, and characterized the effect of an oral glucose challenge on temporal changes in Ser312-phosphofetuin-A in the DIO model. Serum Ser312-phosphofetuin-A concentrations were significantly elevated in DIO mice compared to their control counterparts, and showed a positive correlation with insulin resistance. In response to an oral glucose challenge (OGTT), plasma concentrations of Ser312-phosphofetuin-A levels demonstrated a significant temporal increase in mice fed regular chow. However, in the DIO model, plasma Ser312-phosphofetuin-A concentrations showed a significant temporal decrease. These findings demonstrate that Ser312-phosphofetuin-A concentrations are elevated in insulin resistant conditions, and suggest that phosphofetuin-A may be dynamically involved in the insulin response.