Isoelectric focusing, as a method for molecular separation, is particularly useful since the proteins remain immobilized (focused) in their respective isoelectric points. This aspect is relevant to the simultaneous analysis of genetic markers provided that the corresponding isoelectric points are defined at intervals sufficiently separate and therefore easily distinguished, without causing problems of pattern interpretation. To evaluate isoelectric focusing in combination with immunofixation as a strategy for specific detection and characterization of both polymorphic systems, PLG and F13A, blood samples were obtained from healthy individuals and treated with ethylenediaminetetraacetate-disodium. Results showed that PLG appeared as a multiple-banded pattern. Neuraminidase pretreatment of plasma samples facilitated the distinction of PLG phenotypes. It is concluded that isoelectric focusing is the technique of choice when dealing with simultaneous determination of both PLG and F13A phenotypes. 14 references and 2 figures (Author abstract modified)