In order to define the role of vascular endothelium in the transport and metabolism of adenosine, endothelium-intact and denuded isolated rat aortas were perfused with 3H-adenosine. In the physiological concentration range of adenosine (0.01-1 microM) sequestration of adenosine by endothelium was 90-92%. Similar findings were obtained for inosine. Transfer of radioactive purines from the prelabeled endothelium to the underlying smooth muscle was rather small (1% per hour) and most likely proceeds via dephosphorylated purine compounds. Under steady state conditions the transendothelial adenosine gradient is only moderate because underlying vascular smooth muscle metabolize adenosine less rapidly.