The polymerase chain reaction (PCR) allows the specific amplifica tion of either RNA or DNA nucleotide sequences (1 ,2 ). The hallmarks of this technique are specificity, sensitivity, and speed. The specific ity of the reaction is a result of the requirement of DNA polymerases for a primer that is extended only when annealed to its complemen tary sequence. The primers in the PCR are synthetic oligonucleotides designed to be complementary to the intended target sequence. The sensitivity of PCR is shown by the ability to amplify a target sequence from a single cell under appropriate conditions (3 ). Finally, PCR analy sis is normally rapid; a typical 30 cycle reaction is complete in about 3 h. In addition, the introduction of a thermostable DNA polymerase isolated from Thermus aquaticus (Taq) has allowed the reaction to be automated, greatly increasing the number of samples that can be con veniently processed at once.