Plasma noradrenaline and platelet alpha 2-adrenoceptor density (sites/cell using 3H-rauwolscine with and without phentolamine) were correlated with withdrawal score in 23 hospitalized patients undergoing ethanol withdrawal. Control groups for plasma noradrenaline were 25 patients admitted to hospital for elective gastroscopy and 12 laboratory workers accustomed to venipuncture. Controls for platelet alpha 2-adrenoceptor measurements were a separate group of 31 normal subjects with a mean age close to that of the patients' withdrawing from ethanol. Plasma noradrenaline was significantly higher in the patients undergoing ethanol withdrawal than in patients admitted to hospital for elective endoscopy. Twelve laboratory controls had plasma noradrenaline levels significantly lower than either patient group. A significant though poor statistical correlation existed between ethanol withdrawal score and simultaneously determined plasma noradrenaline level. Platelet alpha 2-adrenoceptor sites/cell were reduced in ethanol withdrawal compared with the normal controls. Platelet alpha 2-adrenoceptor sites/cell increased over the first 24 hr of ethanol withdrawal but remained significantly lower than control values. The change in platelet adrenoceptors was accompanied by a fall in mean plasma noradrenaline. Thus, the stress of hospital admission itself is associated with an increase in plasma noradrenaline, but ethanol withdrawal enhances this increase, which is accompanied by and probably causes a reduction in platelet alpha 2-adrenoceptor numbers. These changes begin to return towards normal within 24 hr as the withdrawal reaction subsides.