A population study in a sample of 200 unrelated individuals from the Basque Country (Northern Spain) was carried out using the GenePrint STR Multiplex System. The PCR products were electrophorized on a denaturing polyacrylamide gel and visualized by silver staining. The loci are TH01, TPOX, and CSF1PO. All loci meet Hardy-Weinberg expectations, and independence of alelles at these STR loci was found. A comparison with other population groups appeared to indicate that frequencies are well conserved in Caucasians, but differ from those of other racial groups. We have also calculated Fst as a measure of population subdivision. No appreciable genetic subdivision in the Caucasian populations studied here was found. Some statistical parameters of forensic interest (Pex, PM and PD) were also calculated. No exclusions were found in 100 mother-child and father-child meiosis. To evaluate the applicability of these systems to forensic casework, we studied the minimum quantity of DNA which can be used applying the multiplex methodology, and the minimum quantity that can be typed in a mixed sample. We also examined several samples such as hair roots, semen stains, vaginal swabs, blood stains and temporary teeth, each of these of varying ages.