Polymerase Chain Reaction (PCR) was developed for a broad range of purposes. As part of developing a very sensitive Immuno-quantitative PCR (iqPCR) assay, we attempted to reproduce two of the published papers, almost always experienced false-positive amplification. Based on personal communication from one of the authors, we suspected that impure reagents were responsible for the false-positive amplification. However, PCR can amplify a small number of DNA into enormous numbers of copies and the possibility of environmental contamination cannot be excluded. In this paper we show that our primers appeared to amplify residual DNA in the Taq DNA polymerase, and induced false-positive results. This finding is not in the published methods papers for iqPCR.