['The mechanism of alcohol-induced syncope is unknown.', 'Head-up tilt tests (HUT: upright at 80 degrees for 30 min) were performed before and after alcohol consumption in 25 patients with unexplained syncope after drinking alcohol. Plasma levels of epinephrine (P-E) and norepinephrine (P-NE) were measured in a supine position and during HUT (at 15 min). Before drinking alcohol, HUT did not provoke neurocardiogenic syncope (NCS) in any of the 25 patients. After drinking alcohol, HUT provoked NCS in 11 patients (alcohol-positive or AP group) but not in 14 patients (alcohol-negative or AN group). Prior to alcohol consumption, P-E and P-NE increased during HUT in both groups, and did not differ significantly between the 2 groups. After alcohol consumption, P-E and P-NE increased during HUT in both group. During HUT, P-NE did not differ between the 2 groups, but P-E was significantly higher in the AP group than in the AN group during HUT (258.0+/-179.2 vs 70.9+/-35.1 pg/ml, p<0.05).'] Does alcohol produce imbalance of adrenal and neuronal sympathetic activity in patients with alcohol-induced neurocardiogenic syncope?