We report here a convenient RT-PCR method to distinguish plasmid human MnSOD cDNA transcripts from the endogenous MnSOD gene products without engineering the cDNA insert. When a specific antisense primer for the carrier vector sequence was paired with a sense primer for the human MnSOD cDNA in RT-PCR analysis, a unique amplicon with the expected size was generated in MnSOD cDNA transfected cells but not in the wild type or vector control cells. The same primers were also used in genomic DNA-PCR to demonstrate genomic incorporation of cDNA in stably transfected cells. This method is convenient and specific in determining exogenous cDNA incorporation and expression in transfectants especially when transcripts of cDNA are difficult to separate from the endogenous mRNA by other methods.