Laboratory experiments were conducted with well-characterized minerals to test the applicability of selective extraction schemes for Se and As partitioning in soils and sediments. Two specific steps were tested: the reductive dissolution of amorphous iron oxides and the oxidation of organic material. Selenium and As associated with amorphous iron oxides were usually not found in solution after reductive dissolution, due to readsorption onto other minerals unaffected by the extractant. Oxidants intended to dissolve organic material also oxidized Se(IV) adsorbed on a mineral to Se(VI), causing the release of Se(VI) to the extractant solution.