In the ten years since the first publication on PCR (Saiki et al. , 1985), this in vitro method of nucleic acid replication and modification has grown to rival in popularity traditional microbiological, genetical und technical procedures for cloning, sequencing, gene detecting and related procedures. To date the PCR literature has emphasized six main areas of application: genetic mapping, detection of mutations, genetic polymorphism, transcriptional splicing and regulation, molecular virology and quantitative procedures. The overwhelming focus of quantification of DNA or RNA by PCR has been on human microbiology and oncological problems. The exquisite sensitivity of PCR gives this method the ability to detect extremely rare DNAs, mRNAs, mRNAs in small numbers of cells or in small amounts of tissue, and mRNAs expressed in mixed-cell populations. However, the exact and accurate quantification of specific nucleic acids in biological samples is in spite of numerous publications in that field still a general problem: during the peR process, an unknown initial number of target sequences are used as a template from which a large quantity of specific product can be obtained. Although the amount of product formed is easy to determine, it is difficult to deduce the initial copy number of the target molecule because the efficiency of the peR is largely unknown.

In 1985, Kary Mullis was driving late at night through the flowering buckeye to the ancient California redwood forest, cogitating upon new ways to sequence DNA. Instead he came upon a way to double the number of specific DNA modules, and to repeat the process essentially indefinitely. 1 He thought of using two oligonucleotide sequences, oppositely oriented, and a DNA polymerase enzyme, to double the number of DNA targets. Each product would thene become the target for the next reaction, effectively yielding a product which doubled in quantity with each repeated cycle. Like the chain reaction leading to nuclear fission, with each cycle event each initial reactant (neutron or DNA molecule) yields two similar products, each of which can serve as the initial reactant. The invention of this exponentially increasing amplification system quickly became known as the polymerase chain reaction (PCR). The tremendous sensitivity of PCR ultimately resides in the necessity for each of two specific oligonucleotide annealing reactions to occur at the same time in the proper orientation. The DNA annealing reaction is a very specific reaction. Single genes have been detected by hybridization of a DNA probe to chromosome preparations together with sensitive fluorescence microscopy. This is the equivalent to detecting a gene present in a single copy per cell genome. It is the combination of two such specific annealing reactions which makes possible the amplification needed to detect a single molecule with a specific DNA sequence in over 100,000 cell genomes.

PCR, developed at Cetus Corporation/USA by Henry A. Erlich, Kary Mullis and Randall K. Saiki, is a very simple method for amplifying nucleic acids in vitro. The realization of this idea bases on the repetition of a set of three different temperatures and yields an increase of the target structure up to a factor of 106 to 1012. Therefore, this technique is predisposed for safe analysis and characterization of DNA and RNA sequences of interest, even where the starting amount of material is enormously small. Because of its sensitivity, speed and versatility this method is particularly suitable for investigations of oncogenes, tumor associated translocations, retroviral sequences, lymphokines and mainly the broad field of degenerative and inflammatory diseases of nervous system. PCR seems to be the technique which could overcome the two most important problems in that field: very small amount of material combined with the necessity of rapid diagnostic procedures in inflammatory infections. "PCR topics" will give an actual overview of basic and applied research fields on usage of polymerase chain reaction. All contributions to this book have been presented at an international congress on "Usage of Polymerase chain reaction in genetic and infectious diseases" which took place in june 1990 in Berlin. The editors wish to thank all participants for their contributions. We offer our thanks and gratitude to our coworkers and especially to our technical assistents Barbara Trampenau, Mirjana Wiirdemann and Hannelore Leonhard.