1 The effect of ACh on the release of adenosine was studied in rat whole carotid bodies, and the nicotinic ACh receptors involved in the stimulation of this release were characterized. 2 ACh and nicotinic ACh receptor agonists, cytisine, DMPP and nicotine, caused a concentration-dependent increase in adenosine production during normoxia, with nicotine being more potent and efficient in stimulating adenosine release from rat CB than cytisine and DMPP. 3 D-Tubocurarine, mecamylamine, DH beta E and alpha-bungarotoxin, nicotinic ACh receptor antagonists, caused a concentration-dependent reduction in the release of adenosine evoked by hypoxia. The rank order of potency for nicotinic ACh receptor antagonists that inhibit adenosine release was DH beta E > mecamylamine > D-tubocurarine > alpha-bungarotoxin. 4 The effect of the endogenous agonist, ACh, which was mimicked by nicotine, was antagonized by DHbE, a selective nicotinic receptor antagonist. 5 The ecto-5'-nucleotidase inhibitor AOPCP produces a 72% inhibition in the release of adenosine from CB evoked by nicotine. 6 Taken together, these data indicate that ACh induced the production of adenosine, mainly from extracellular ATP catabolism at the CB through a mechanism that involves the activation of nicotinic receptors with alpha 4 and beta 2 receptor subunits.