The exponential amplification of small amounts of nucleic acids makes polymerase chain reaction (PCR) not only powerful but also challenging as a quantitative method. Variations in nucleic acid preparation, thermal cyclic performance, the choice of the polymerase, and the amplification procedure can cause large differences in final product yield. To address the challenges of quantitative PCR, the procedure has been critically examined, leading to an understanding of the critical parameters involved in quantitative amplification. Accepted parameters can be summarized as a series of choices: external vs internal standard, exogenous vs endogenous standard, competitive vs noncompetitive amplification, and exponential vs plateau amplification (1–3).