We tried to characterize nicotinic acetylcholine receptors involved in the release of catecholamines from the rat adrenal gland. The isolated adrenal gland was retrogradely perfused via the adrenal vein with Krebs-Ringer solution at a flow rate of 0.5 ml/min. Endogenous catecholamines, adrenaline and noradrenaline, released into the perfusate were electrochemically measured using high-performance liquid chromatography. (-)-Nicotine (3x10 - 6 -3x10 - 5 M) evoked the release of catecholamines (adrenaline noradrenaline) in a concentration-dependent manner. The (-)-nicotine (10 - 5 M)-induced release of catecholamines was effectively attenuated by mecamylamine (10 - 7 and 10 - 6 M) (a relatively selective antagonist of α3β4 nicotinic receptors), but not influenced by α-bungarotoxin (3x10 - 7 M) (an antagonist of α7 nicotinic receptors) and dihydro-β-erythroidine (10 - 5 M) (a relatively selective antagonist of α4β2 nicotinic receptors). (+/-)-Epibatidine (3x10 - 7 and 10 - 6 M) (a non-selective nicotinic receptor agonist), (-)-cytisine (10 - 5 and 10 - 4 M) (an agonist of β4 nicotinic receptors) and (+/-)-2-(3-pyridinyl)-1-azabicyclo(2.2.2)octane (RJR-2429) (10 - 5 M) (a putative agonist of α3β4 nicotinic receptors) effectively evoked the release of catecholamines (adrenaline noradrenaline), while (E)-N-methyl-4-(3-pyridinyl)-3-butene-1-amine (RJR-2403) (up to 10 - 4 M) (a selective agonist of α4β2 nicotinic receptors) had no effect. The efficacies of these agonists are as follows: (+/-) epibatidine RJR-2429>(-)-cytisine>(-)-nicotine RJR-2403. These results suggest that α3β4 nicotinic receptors are involved in the release of catecholamines from the rat adrenal gland.