Results From a Single qPCR Assay can be Difficult to Interpret. In this experiment, a set of 120 Dicer-substrate RNAs (DsiRNAs) were used for RNAi targeting of the 5’ UTR, coding sequence (CDS), and 3’UTR of “Gene X” mRNA; their positioning is indicated by the colored X axis bar. mRNA knockdown was measured using 2 qPCR assays, one amplifying a region near the 5’ end of the coding sequence of “Gene X” (Assay 1, red diamonds), and the other amplifying a fragment in the 3’ UTR (Assay 2, blue circles). The percentage of “Gene X” mRNA detected by Assay 1 varies, depending on the DsiRNA target site. These data demonstrate that when DsiRNAs that targeted more 3’ “Gene X” positions were used, the expression levels detected by the 5’ and 3’ qPCR assays were significantly different. This result exemplifies the importance of using more than one qPCR assay per target to identify one that will provide a consistent measure of mRNA expression knockdown. Multiplex qPCR is an efficient, cost-effective method for analyzing several such assays in a single reaction.