The Phospho-p90RSK(Thr573) Colorimetric Cell-Based ELISA Kit is a convenient, lysate-free, high throughput and sensitive assay kit that can detect Phospho-p90RSK(Thr573) protein expression profile in cells. The kit can be used for measuring the relative amounts of Phospho-p90RSK(Thr573) in cultured cells as well as screening for the effects that variuos treatments, inhibitors (ie siRNA or chemicals), or activators have on Phospho-p90RSK(Thr573).