[en] After the aldosterone fraction of plasma was specifically absorbed using highly concentrated anti-aldosterone serum(i.e. Ab-II; diluted to 1:50,000), it was applied to the radioimmunoassay: and the separation of the free from the bound fractions was performed by the saturated ammonium sulfate method. Reasonable and satisfactory standard curves were obtained, but attention should be given to environmental factors at measurement, especially to the room temperature in summer. According to our results the mean final recovery for 58 specimens was 41.8+-6.4(SD)% through the overall extraction procedure, and the minimum detectable sensitivity of the standard curve was 10pg. The mean water blank value was 7.02+-2.62 (SD) pg/tube. Possible reasons for the higher blank value than others may have been the reagent or the solvent blank, and/or the insufficient process of immunologic purification by Ad-II for the tritium-labelled aldosterone which was used for recovery and immunoassay. The precision was from 9.4 to 25.3% coefficient of variations; the accuracy and recovery rate were almost satisfactory. In our clinical application, the plasma aldosterone concentration indicated high values in the peripheral and affected adrenal venous blood of patients with primary aldosteronism. In a patient with Bartter's syndrome, hyperreninemia and secondary hyperaldosteronism were observed. Almost all of the patients with Addison's disease and with total adrenalectomy indicated the lowest or undetectable levels. A high level of plasma aldosterone concentration was measured in a patient with edema and chronic renal failure and one with juvenile hypertension associated with an orbital tumor. (JPN)