The stereoisomers of oxazepam sodium hemisuccinate have been tested for their ability to inhibit the [3H]adenosine binding in guinea-pig brain synaptosomes. 2. All three stereoisomers were able to inhibit the [3H]adenosine binding in a dose-dependent fashion. 3. The IC20 values of the D-, DL- and L-stereoisomers were approximately 5 X 10(-5) M, 7.5 X 10(-5) M and 10(-4) M respectively. 4. The results are consistent with hypothesis that adenosine may be the endogenous substrata mediating some actions of the benzodiazepines.