The IRS-1 (Phospho-Ser639) Colorimetric Cell-Based ELISA Kit provides a lysate-free, convenient, and high-throughput approach for sensitive detection of IRS-1 (Phospho-Ser639) protein expression profile in cells. The kit can be used for measuring the relative amounts of IRS-1 (Phospho-Ser639) in cultured cells as well as screening for the effects that various treatments, inhibitors (ie siRNA or chemicals), or activators have on IRS-1 (Phospho-Ser639).