A comparison of sizing precision of Profiler Plus loci analyzed with GS500 and ILS600 internal standards for intercapillary runs found that for all analyzed loci, precision obtained with ILS600 was significantly better than with GS500. Similar results were obtained for loci present in another commonly used kit, SGM Plus. In examining the correlation of retention time with allele sizes for three analyzed internal DNA standards, it was found that if better correlation of internal standard DNA lengths with peak arrival time exists, then better calibration curves and thereby sizing can be achieved. The influence of different internal standards on sizing accuracy was also analyzed. A very high correlation was observed between the true sizes and the sizes obtained with both internal standards; however, in the case of the GS500, the average size difference between actual and observed sizes was almost 2 nt and in the case of the ILS600, almost 5 nt, indicating that the ILS600 provides better precision of analysis than the GS500, but worse sizing accuracy. From a forensic genetics perspective, precision of analysis is more important that sizing accuracy. In analyzing the effect of two commercially available matrixes (POP4 and POP6) on precision analysis, the use of POP6 increased precision sizing substantially, possibly because of a higher concentration of the separation matrix and a better sieving effect than POP4 gel. The descriptions of materials and methods address the analyzed samples, capillary electrophoresis on AB1310 Genetic Analyzer, and statistical calculations. 4 figures, 1 table and 24 references