1 The pressor responses to injected noradrenaline (NA) of isolated perfused femoral or renal arteries of the rabbit were studied.2 Vascular smooth muscle is relatively resistant to hypoxia. A combination of hypoxia and dinitrophenol (DNP) respiratory uncoupling was necessary to abolish the pressor response to NA. Loss of the pressor response was assumed to result from decreased capacity of arteries to form adenosine 5'-triphosphate (ATP). Reperfusion of the hypoxic arteries with oxygenated medium resulted in recovery of the pressor response to NA.3 Inclusion of inosine (10 mM) in the hypoxic perfusion medium increased significantly the rate and extent of post-hypoxic recovery of the pressor response to NA.4 Whereas the presence of inosine in the hypoxic perfusion medium aided post-hypoxic recovery, inosine had no direct action on the pressor dose response to NA. Therefore, the action of inosine was protective as opposed to direct.5 The protective action of inosine did not involve potentiation of NA binding to NA-adrenoceptor sites (the equilibrium coefficient, K(eq) for NA-receptor interaction was unaltered by hypoxia and/or inosine).6 The results are discussed in terms of a presumptive mechanism whereby inosine is believed to act by maintaining intracellular adenine nucleotide concentrations in hypoxia.