The polymerase chain reaction (PCR) uses two oligonucleotide primers to direct the synthesis of specific sequences of DNA. One primer anneals to
the coding strand of DNA and the other to the anticoding strand; the primer
binding sites are typically separated by a few hundred base pairs (100-
1000 bp). Repeated cycles of polymerization and denaturation lead to the
exponential increase of the sequence defined by the pnmers. The extraordi-
nary sensitivity and specificity of PCR have established it as a standard tech-
nique in molecular biology in the short time since it was first described (1).
The purpose of this chapter is to suggest starting conditions for a PCR
reaction and ways to overcome the main problems in PCR. It is intended as a
practical guide, so theoretical aspects will not be discussed in detail. For a
fuller accoun t, there are excellent and comprehensive guides edited by Erlich
(2) and by Innis et al. (3). Protocols for special applications of PCR are de-
scribed in later chapters in this volume.