Sequential use of reverse transcriptase and the polymerase chain reaction (RT-PCR) permits rapid and sensitive detection of specific RNAs. However, the greatest advantage of RT-PCR, its remarkable sensitivity, has also limited its usefulness in quantitative applications, since the effects of minor variations in reaction conditions from sample to sample are greatly magnified during the amplification process. Several recently developed techniques circumvent this problem, allowing accurate quantitation of RNA using RT-PCR.