Ethidium bromide-stained DNA products of QC-PCRs using 105 CD15+ or 105 CD15− cells and 8, 40, 200, or 1,000 copies of an identical competitor target sequence were analyzed by agarose gel electrophoresis. Results for patients (pt) 1, 4, 5, and 8 are shown. The concentration in copy numbers of EBV genomes detected is shown below each panel.