PCR is an enabling and preferred technology for the detection of DNA or mRNA in genomic age, and has been widely used in molecular medicine, biotechnology, microbiology and diagnostics. PCR has many excellent traits, such as high specificity and sensitivity, short handle time, reliable and effective results, low demand for sample. In recent years, real-time reverse transcription PCR (qRT-PCR) has acquired an impressive improvement in the detection of mRNA, it has a perfect sensitivity and can quantify some rare mRNA copies as low as less ten. The progress in PCR results in a more strict demand for sample, so it is necessary to take the potential PCR-inhibitory components in peripheral blood and bone marrow samples into account again. This review explores the potential PCR-inhibitory components in peripheral blood and bone marrow samples, and discusses the possible mechanism and solutions for the inhibition effect, also emphasizes the potent effect of the frequently-used anticoagulant heparin sodium in PCR. This article will be helpful to assess the PCR detection results (especially qRT-PCR ) in some degree, for example, can use it to decide whether the PCR detection results are reasonable for some low-expression genes, or use it to eliminate the false negative results generated by PCR-inhibitory components in sample.