Cells transfected by retroviral vectors are brought in agene of particular interest and are very useful in avariety of experiments. It is essential to testify that theDNA fragment was successfully introduced into the cellstogether with the retroviral vectors. Polymerase chainreaction is believed to be a fast and convenient method forthis purpose when using primers flanking the cloning siteof the inserted DNA. Unfortunately, a single PCR reactionoften fails to amplify the targeted fragment because of theexistence of endogenous virus DNA in cell genome. However,in this study we conducted a procedure for a single PCR,using vector-specific primers as well as a nested PCR, andsuccessfully detected the DNA fragments cloned in MFGretroviral vectors in 22 transfected cell lines. We alsoproved that real time quantitative PCR in combination withMFG-specific primer is useful to determine copy number ofthe retroviral vector in murine producer cell lines.