Summary A simple, economical method is described for the radioimmunoassay of cortisol in serum. Extraction is avoided by heating the diluted serum to inactivate cortisol-binding globulin. The radioimmunoassay is carried out in a single disposable scintillation vial without centrifugation. Free and bound steroid is separated by partition between ammonium sulphate solution and liquid scintillation fluid. Accuracy, precision and sensitivity are satisfactory. Normal ranges obtained are comparable to those obtained by other radioimmunoassay methods for cortisol.
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