A sensitive method to measure activities of firefly & Renilla luciferases sequentially from a single sample. The firefly luciferase reporter is measured first by adding LAR II to generate a stabilized luminescent signal. After quantifying the firefly luminescence, this reaction is quenched, & the Renilla luciferase reaction is simultaneously initiated by adding Stop&Glo® Reagent to the same tube. The Stop&Glo® Reagent also produces a stabilized signal from the Renilla luciferase.