A laboratory method used to make many copies of a specific genetic sequence for analysis or other studies. It uses an enzyme called reverse transcriptase to change a specific piece of RNA into DNA, which can be amplified (made in large numbers) by another enzyme called DNA polymerase. Reverse transcription-polymerase chain reaction may be used to look for certain changes in a gene or chromosome, which may help diagnose a disease, such as cancer. It may also be used to study the RNA of certain viruses, such as the human immunodeficiency virus (HIV) and the hepatitis C virus, to help diagnose and monitor an infection. Also called RT-PCR.