The present invention relates to hydrophilic, high quantum yield acridinium compounds. It has been discovered that the placement of electron-donating groups in the acridinium ring system increases the amount of light that is emitted by the corresponding acridinium compound when its chemiluminescence is triggered by alkaline peroxide. More specifically, it has been found that the placement of one or two hydrophilic, alkoxy groups at the C-2 and/or C-7 position of the acridinium ring system of acridinium compounds increases their quantum yield and enhances the aqueous solubility of these compounds. The present hydrophilic, high quantum yield, acridinium compounds are useful chemiluminescent labels for improving the sensitivity of immunoassays.