555 blood samples from different areas of the Costa Rican territory was studied by electrophoretic analysis to determine the phenotypic and genotypic frequencies of 10 polymorphic allozimes (PGM sub, EsD, AK, EAP, Glol, ADA, CA II, PepA, Gc y Tf). There are no significant differences between the expected distribution and the ones found according to the Hardy-Weimberg Law. The results are comparable with other population studies that include North American Caucasian and Hispanic populations. The calculation of the discrimination power is useful in forensic science and the values obtained in EsD, Glo I, PGM sub EAP and Gc make these markers an useful probabilistic tool in the Administration of Justice.