1. Almost all steroids, occurring in the Cohn's protein fraction of IV-1, were of conjugated forms with α-globulin, but not in free forms.
2. Almost all of such bound steroids were dissociated from the serum protein by the treatment of paper electrophoresis, and hydrolysis, but some were still remaining as the conjugated forms even after these treatments.
3. By the examinations of standard with reference Rf values, fluorescent color and ultraviolet absorption maxima of steroids obtained by paper electrophoresis, relatively small amounts of Comp. F, B and S could be measured in Vp, that represents the peak for absorption of steroids originated from corticoids as previously reported, while those of testosterone, androsterone, dehydroisoandrosterone, progesterone and Comp. F could be measured in IVp, originated from androgens.
4. Comp. F, Q, S, A, testosterone, dehydroisoandrosterone, androsterone and progesterone were respectively detected in acid-hydrolyzates of this fraction.
5. The fraction IV-1 showed the highest 17-ketosteroid concentrations, possibly suggesting that the protein-bound 17-ketosteroid of plasma was mainly conjugated with the α-globulin.