The Cytochrome P450 21A2 Colorimetric Cell-Based ELISA provides a lysate-free, convenient, and high-throughput approach for sensitive detection of CytochromeP45021A2 protein expression profile in cells. The kit can be used for measuring the relative amounts of CytochromeP45021A2 in cultured cells as well as screening for the effects that various treatments, inhibitors (ie siRNA or chemicals), or activators have on CytochromeP45021A2.