A procedure has been elaborated to measure the trace element selenium (Se) in onions and potatoes consumed in the Algiers region. The important chemical pre-concentration step includes wet sample oxidation and the reduction of Se to the element using co-precipitation with tellurium as carrier element and radioactive 7 5 Se to control the chemical process yield. Finally, the filtered probe material is dissolved, labeled with yttrium as an internal PIXE standard and deposited on a thin foil of polycarbonate by solvent drip evaporation. The resulting targets are investigated by the PIXE analysis with 3-MeV proton beams. The low concentration of Se in the samples is determined by measuring the characteristic X-rays.