1. When tested at concentrations resulting in significant inhibitions of adenosine uptake in brain slices, diazepam and several other benzodiazepines were without effect on brain adenosine kinase. 2. This suggests that the inhibitory effect of the benzodiazepines on adenosine accumulation is at the membrane transport level and not by an inhibition of the intracellular phosphorylation step which facilitates adenosine uptake.