In order to increase the power of discrimination for human identification purposes, Promega Corporation developed the GenePrint PowerPlex 2.1 system, (a nine-locus short tandem repeat (STR) multiplex), and tested a separate pentanucleotide-repeat locus, Penta D. As with PowerPlex 1.1, PowerPlex 2.1 is based on a two-color detection of fluorescent-labeled DNA products amplified by polymerase chain reaction and provides a valuable tool for accurate and rapid allele determination. To meet the Quality Assurance Standards for Forensic DNA Testing Laboratories, the study tested the efficiency and reproducibility of the PowerPlex 2.1/Penta D system by several validation studies conducted as a joint project among seven laboratories. Validation tests included concordance studies, sensitivity, series specificity determination, as well as performance in forensic and environmentally affected samples. Test results demonstrated the consistency and reliability of the PowerPlex 2.1/Penta D system. Figures, tables, references