The GeneScan™ 500 ROX™ Size Standard is an internal lane size standard developed for use with the Applied Biosystems fluorescence-based DNA electrophoresis systems. The use of an internal lane size standard enables automated data analysis and is also essential for achieving high run to run precision in sizing DNA fragments by electrophoresis. GeneScan™ 500 ROX™ Size Standard is designed for sizing DNA fragments in the 35-500 bp range and provides 16 single-stranded ROX™ dye labeled fragments of 35, 50, 75, 100, 139, 150, 160, 200, 250, 300, 340, 350, 400, 450, 490, and 500 bases. Each of the DNA fragments is labeled with a proprietary fluorophore, which results in a single peak when run under both denaturing and non-denaturing conditions.