The polymerase chain reaction is a powerful and versatile tool for the analysis of nucleic acids. Through a reaction imitating in vivo DNA replication, a defined fragment of DNA is repeatedly replicated by a DNA polymerase in an exponential manner. Such selective amplification of a sequence of interest has created new possibilities in molecular biology and related sciences. The basic principle and some of its variations and applications for both qualitative and quantitative analyses of potential interest to dermatologists are described.