The study found that allele sizes were smaller when ambient temperature increased and larger when ambient temperature decreased. This was apparently due to an increased mobility exhibited by Profiler Plus alleles relative to GS-500 fragments as ambient temperature increased. This phenomenon is most pronounced with the 250- and 340-based fragments of the GS-500 sizing standard. This is probably due to the varying sequence content between the size-standard fragments and the DNA sequences that are actually measured. The study found that when ambient temperature varied, a sample analysis method change improved precision. The authors suggest that the Global Southern method may provide improved precision over the Local Southern method when using the GS-500 internal standard with the ABI Prism 310 Genetic analyzer. In addition, precision for fragments greater than 300 bases is further improved by excluding the 340-based GS-500 fragment in conjunction with using the Global Southern method. When ambient temperature shifts occurs, this sizing method change should reduce the number of sample reruns required. The description of materials and methods includes sample preparation and electrophoresis for the ABI Prism 310 Genetic Analyzer and descriptions of the alternative approaches tested. The latter included analyses that omitted the 340-base fragment, an investigation into the use of Global Southern, and an evaluation of the size standards GeneScan-400HD and Internal Lane Standard 600. All sample files were analyzed with the ABI Prism GeneScan v2.1 or v3.1 software, using both the Local and Global Southern sizing methods. 6 figures and 11 references