Transcriptional activity within a cell can be used to evaluate cell response to a ligand or promoter activity within a transgene or plasmid within a cell. Catalent has developed a relative potency bioassay using real-time quantitative reverse transcription (RT-qPCR) in a duplex format to assess relative transcription activity in cells treated with ligands or transgenic vectors. The assay utilizes two fluorescent dyes with minimally overlapping emission spectra that allow real-time monitoring of the gene expression of both target and normalizer genes. The assay does not require purification of the mRNA produced by the cells once lysis has occurred. Normalizing the qPCR cycle thresholds (CT) of the target transcript to the reference transcript allows response curve to be generated and compared to a reference standard. The generation of a four-parameter fit curve analysis from raw qPCR cycle threshold data allows for comparison of relative potency and assessment of suitability based on curve parallelism. The assay platform has been used by Catalent to qualify a repeatable, accurate, linear, and specific bioassay for assessing relative potency.