This p300 Cell Based ELISA Kit allows for the detection of p300 and the effects that certain stimulation conditions have on p300 expression in different cell lines. Qualitative determination of p300 concentration is achieved by an indirect ELISA format. In essence, the p300 is captured by Anti-p300 Antibodies which in turn are detected by HRP-conjugated secondary antibodies. Through this binding, the HRP enzyme (conjugated to the secondary antibody) can catalyze a colorimetric reaction upon substrate addition. Due to the qualitative nature of this p300 Cell Based ELISA Kit, multiple normalization methods are described: 1) Anti-GAPDH Antibody is included to serve as an internal positive control in normalizing the target absorbance values. 2) Following the colorimetric measurement of HRP activity via substrate addition, the Crystal Violet whole-cell staining method is used to determine cell density. After staining, the results can be analyzed by normalizing the absorbance values to cell amounts, by which the plating difference can be adjusted.