Previously several selenium-containing proteins with different subunit molecular masses (M r ) were detected in the arterial wall and brain of rats. In continuation of this work, after labeling of rats in vivo with [ 75 Se]selenite, the new selenium-containing proteins of interest were purified on a Sephadex G-200 column followed by preparative isoelectric focusing. Nuclear analytical methods (γ-counter and γ-detector) were applied in the detection and identification of the 75 Se-labeled proteins. The two 75 Se-containing proteins from the arterial wall migrated as 15.0- and 67.0-kDa species on SDS–PAGE gels with pI values of 4.5 and 5.1, respectively. The three 75 Se-containing proteins from brain purified to homogeneity had M r values of 18.0, 30.0, and 42.9 kDa and pI values of 6.3, 6.5, and 6.0, respectively. Of these proteins, the 67.0-, 42.9-, and 30.0-kDa species may be yet not characterized selenoproteins with important biological functions.