Polymerase chain reaction (PCR) is a type of test that can identify specific types of genetic material (DNA) in a small sample.

PCR is useful for many purposes, such as for:

• Finding out what type of bacteria, virus, or fungus is causing an infection.
• Law enforcement, to identify a person who may have committed a crime.
• Looking at a person's DNA and determining if that person has a change (mutation) in his or her DNA that may cause disease.

PCR works by taking a small sample containing DNA and using an enzyme called a polymerase to make many copies of that DNA. The process of copying the DNA is done in cycles that are repeated up to 30 times or more. Millions or even billions of copies of the DNA may be made during PCR.