The distributioa of Se in Hb and the effects of Se intake and its chemical forms oil the distribution were studied. The results showed that Se in human Hb was all located in globin and divided equally in a and ? chains. However, a part of Se could fall from Hb during the process of isolation when more Se as SeMet was taken and "excess" Se appeared in Hb. It was implicated that there were at least two kinds of linkage between Se and Hb --tight and loose.Regarding the components of amino acid in ? and ? chains, we assumed that a tight linkage between Se and Hb was in the form of SeMet, which was incorporated into Hb by dietary Se during the synthesis of Hb; the loose linkage was formed by a part of "excess" Se and CyS, especially No.93 CyS in ? chain, being unstable sclcnotrisulf ide or selenopersulfide, which broke easily by reduction during isolation. They might be utilized first by human body when Se was required.