A rapid, sensitive and specific radioreceptor assay for measuring benzodiazepines in plasma and other biological specimens without sophisticated equipement or methodology. This method is based on the competition between [<s3>sH] diazepam or tritiated flunitrazepam and pharmacologically active benzodiazepines present in plasma, for binding sites on rat brain synaptosomal membranes. No interference is obtained with drag-free plasma or plasma samples containing high concentrations of other commonly used drugs. High correlations (r = 0.98;p < 001) were obtained between the 'diazepam equivalents' measured in plasma using the radioreceptor assay and the levels of diazepam and N-demethyl diazepam obtained by gas-liquid chromatography. The radioreceptor assay is useful in monitoring blood benzodiazepine levels for both therapeutic and toxicologic purposes. 
RADIO RECEPTOR ASSAY FOR BENZODIZAPINES IN PLASMA AND OTHER BIOLOGICAL SPECIMENS