The effects of a number of interventions influencing sympathetic nervous activity on the severity of coronary artery reperfusion-induced arrhythmias in anaesthetised rats have been examined. Noradrenaline (0.1 microgram kg-1 min-1) reduced the mortality that usually occurred as a consequence of ventricular fibrillation. Isoprenaline (5 micrograms kg-1) did not significantly affect the severity of reperfusion-induced arrhythmias, although arrhythmias occurring during the 5-min period of ischaemia were exacerbated. The alpha-adrenoceptor antagonist nicergoline (0.25 and 0.5 mg kg-1 min-1) markedly suppressed both the ventricular tachycardia and fibrillation occurring upon release of the occlusion, whereas prazosin (1.0 mg kg-1) only slightly reduced the incidence of ventricular tachycardia. The beta-adrenoceptor antagonists atenolol and timolol did not significantly modify the severity of these reperfusion-induced arrhythmias. Pretreatment with reserpine (0.1 mg kg-1) or 6-hydroxydopamine (20 mg kg-1), which depleted myocardial catecholamine concentrations by 90%, had no effect on the indices of arrhythmic activity. Similarly, administration of L-thyroxine (1 mg kg-1) or propylthiouracil (50 mg kg-1) on 7 consecutive days prior to coronary artery occlusion did not alter the incidence of arrhythmias occurring upon reperfusion. Taken as a whole, these results do not suggest an important role for sympathetic nervous activity in the genesis of reperfusion-induced arrhythmias in anaesthetised rats.