SUMMARY: The specificity of the steroid-binding β-globulin obtained from pregnancy plasma was studied by comparing the [6,7-3H]oestradioldisplacing effect of various steroids in a system consisting of a solution of the protein and Sephadex G-10. It seems that steroid binding is not limited to oestradiol or to testosterone but that most 17β-hydroxysteroids are bound to a similar degree.