The pharmacokinetic parameters and the time course of the effect after acute oral administration of yohimbine on salivary secretion in patients treated with tricyclic antidepressants were investigated. Yohimbine (10 mg) increased both salivary outflow and plasma noradrenaline levels for 4 h. Pharmacokinetic parameters (ti/2, tmax, Cmax and AUCexp) and plasma concentrations of noradrenaline were higher in patients treated with tricyclic antidepressants than in controls. At this dose, yohimbine induced a relatively large number of side effects. A lower dose (4 mg) increased salivary secretion for 3 h without any side effects in patients treated with tricyclic antidepressants but not in healthy volunteers. These data describe an interaction between yohimbine and tricyclic antidepressants and thus show that a relatively low dose (4 mg) of yohimbine could be useful in the treatment of dry mouth due to tricyclic antidepressants.