A real-time PCR procedure is proposed for assaying E. coli residual DNA in the pharmaceutical substance of human recombinant insulin. For the quantitative analysis of the DNA content, an amplification of fragments of the bla gene plasmid DNA and E. coli genomic DNA of the 16S RNA gene were used. The contents of plasmid and genomic DNA were detected both in intermediates at various stages of the insulin purification process and in the finished product. © 2010 Pleiades Publishing, Ltd.