It is well-known that dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S) are the major C 19 -secretory products of the human adrenal cortex. The measurement of these steroids in plasma may serve as a possibly superior index in assessing biologic function of adrenal.However one of the disadvantages of competitive protein binding assays and radioimmunoassays (RIA), which have usually been used, exists in the need for preliminary extraction or troublesome purification of steroids. Now, RIA method which do not require any extraction or chromatographic purification have been developed. Antiserum I and II were derived from rabbits immunized by 11α-succinoyloxy-DHEA-BSA and DHEA 3-succinate-BSA, respectively. Antiserum I was highly specific to DHEA and was used for determination of DHEA, and its reactivity titer was 1 : 2,000. Antiserum II was used for DHEA-S assay at dilution of 1 : 60,000.Comparison experiment on plasma samples were carried out as follows.1) DHEA in plasma was determined by RIA using antiserum I for samples obtained by the method A and B.A : DHEA was extracted from plasma with ether and purified by chromatography (Sephadex LH-20).B : The sample was obtained by extraction as a similar described above (without chromatography). 2) DHEA-S in plasma was determined using antiserum I (C) and antiserum II (D and E) for samples obtained by the method C, D and E.C) DHEA-S was hydrolyzed by acid and DHEA thus obtained was purified by the method A.D) A saturated ammonium sulfate was added to plasma and DHEA-S was extracted with ethyl acetate.E) Plasma was directly used for RIA.All results were found to be fully reliable. Coefficient of correlation in A-B, C-D and C-E were 0.965, 0.858 and 0.880, respectively.It was found that RIA methods for obtained by method B and E are very useful for clinical application.