In molecular biology, real-time polymerase chain reaction, also called quantitative real time polymerase chain reaction (Q-PCR/qPCR) or kinetic polymerase chain reaction, is a laboratory technique based on the polymerase chain reaction, which is used to amplify and simultaneously quantify a targeted DNA molecule. It enables both detection and quantification (as absolute number of copies or relative amount when normalized to DNA input or additional normalizing genes) of a specific sequence in a DNA sample.

The procedure follows the general principle of polymerase chain reaction; its key feature is that the amplified DNA is quantified as it accumulates in the reaction in real time after each amplification cycle. Two common methods of quantification are: (1) the use of fluorescent dyes that intercalate with double-stranded DNA, and (2) modified DNA oligonucleotide probes that fluoresce when hybridized with a complementary DNA.

Frequently, to measure gene expression, real-time polymerase chain reaction is combined with reverse transcription to quantify messenger RNA (mRNA) in cells or tissues.

Abbreviations used for real-time PCR methods vary widely and include RTQ-PCR, Q-PCR or qPCR. ^[1] Real-time reverse-transcription PCR is often denoted as qRT-PCR,^[2], RRT-PCR,^[3] or RT-rt PCR.^[4] The acronym RT-PCR commonly denotes reverse-transcription PCR and not real-time PCR, but not all authors adhere to this convention.RT-PCR or reverse transcription PCR refers to PCR that uses product of an RT reaction as template. In effect, the PCR amplifies cDNA fragments. In one-tube RT-PCR, RNA and PCR primers are added to a reaction mix that is thermocycled for RT first followed by for PCR. One-tube RT-PCR reaction mixes are supplied by many manufacturers. Drawbacks to their use include lack of flexibility. Otherwise, RT-PCR is a two step process