The NPM (Phospho-Ser4) Colorimetric Cell-Based ELISA Kit provides a lysate-free, convenient, and high-throughput approach for sensitive detection of NPM (Phospho-Ser4) protein expression profile in cells. The kit can be used for measuring the relative amounts of NPM (Phospho-Ser4) in cultured cells as well as screening for the effects that various treatments, inhibitors (ie siRNA or chemicals), or activators have on NPM (Phospho-Ser4).