The PowerPlex() ESX 16 System combines the 11 loci compatible with the UK National DNA Database, contained within the AmpFlSTR() SGM Plus() PCR Amplification Kit, with five additional loci: D2S441, D10S1248, D22S1045, D1S1656 and D12S391. The multiplex was designed to incorporate these five new loci as mini- and midi-STRs while maintaining the loci found in the AmpFlSTR() SGM Plus() kit as standard size. The PowerPlex() ESX 17 System amplifies the same loci as the PowerPlex() ESX 16 System, but with the addition of a primer pair for the SE33 locus. Tests were designed to address the developmental validation guidelines issued by the Scientific Working Group on DNA Analysis Methods (SWGDAM), and those of the DNA Advisory Board (DAB). Samples processed include DNA mixtures, PCR reactions spiked with inhibitors, a sensitivity series, and 306 United Kingdom donor samples to determine concordance with data generated with the AmpFlSTR() SGM Plus() kit. Allele frequencies from 242 White Caucasian samples collected in the United Kingdom are also presented. The PowerPlex() ESX 16 and ESX 17 Systems are robust and sensitive tools, suitable for the analysis of forensic DNA samples. Full profiles were routinely observed with 62.5pg of a fully heterozygous single source DNA template. In mixture analysis, a range of 52-95 percent of unique minor contributor alleles was observed at 19:1 mixture ratios where only 25pg of the minor component was present. Improved sensitivity combined with the robustness afforded by smaller amplicons has substantially improved the quantity of information obtained from degraded samples, and the improved chemistry confers exceptional tolerance to high levels of laboratory prepared inhibitors. (Published Abstract)