The MEK1 (Phospho-Thr291) Cell-Based ELISA Kit is a convenient, lysate-free, high throughput and sensitive assay kit that can monitor MEK1 (Phospho-Thr291) protein expression profile in cells. The kit can be used for measuring the relative amounts of MEK1 (Phospho-Thr291) in cultured cells as well as screening for the effects that various treatments, inhibitors (ie. siRNA or chemicals), or activators have on MEK1 (Phospho-Thr291) .