The most innovative technique introduced recently into the field of biological study is the polymerase chain reaction (PCR) which can amplify even single-copy DNA sequences to high levels. In Situ PCR, which is a method of in Situ amplification of DNA of interest in tissue sections, has been subsequently developed and mainly used to investigate tissues infected with viruses. A combination of reverse transcription and PCR has been utilized to detect mRNA of interest in Situ. The technique of in Situ PCR is promising for a wide variety of applications in basic histology and histopathology.