Selenium (IV) can be quantitatively extracted at trace concentrations with 2-thenoyltrifluoroacetone-xylene (0.03 M) at pH 1.0–4.5. It is determined in the organic phase photometrically by complexation with 3,3′-diaminobenzidine. The system conforms to Beer's law in the concentration range of 22–132 μg/ml of selenium. The complex is stable. Salting-out agents have no effect on extraction. Selenium can be extracted and determined in one operation in the presence of several elements.