The inhibition of 3Hnitrobenzylthioinosine (3HNBI) binding to human parietal cortex membranes by adenosine transport inhibitors, adenosine receptor agonists and antagonists and dihydropyridines was investigated. While the adenosine transport inhibitors inhibited 3HNBI binding with Ki values in the low nanomolar range and the adenosine A1 receptor agonist, cyclopentyladenosine, with a Ki in the low micromolar range, no IC50 values could be obtained for the adenosine receptor antagonists at concentrations up to 100,000 nM. Among the dihydropyridines (+)-nimodipine was the most potent with a Ki of 201 +/- 55 nM. Inhibition of adenosine transport thus may contribute to the clinical effects of nimodipine in the central nervous system.