1. Vasodilatation induced by adenosine is mediated through the activation of A2-purinoceptors in endothelial and smooth muscle cells. 2. Adenosine induces a rapid and transient membrane hyperpolarization in endothelial cells. 3. Acute exposure to adenosine or A2-purinoceptor agonists activates the L-arginine-NO signalling pathway in human endothelial cells in vitro.