Randomly amplified polymorphic DNA (RAPD) is a technique that is useful as a rapid means of comparing and discriminating the DNA from different individuals. RAPD is based on random priming--the use of short pieces of DNA that bind to many random places in the genome. The DNA is then fragmented using restriction enzymes. Because of the small size of the probe DNA and the many fragments that can be generated, a very large number of reaction products can be obtained. The products can be separated based on their size by electrophoresis and detected by staining of the gel or, if the primers are radioactive, by the technique of autoradiography.

RAPD has been combined with the polymerase chain reaction (PCR). The use of PCR allows the DNA to the probe bound to be amplified in number to detectable levels, and so eliminated the need for a large amount of DNA at the commencement of an experiment. Older techniques, like restriction fragment length polymorphism, require large amounts of genomic DNA, are difficult to automate and require much time to complete.

RAPD has found a place as a technique for the rapid and preliminary examination of DNA. While useful in this regard, PCR-based fingerprinting techniques relying on random primers are not robust and generally are unsuitable for use as population markers, particularly in critical or demanding situations such as human diagnostics or courtroom evidence. RAPD has proved useful in discriminating genotypes of various prokaryotic and eukaryotic species.