The local anaesthetic and haemodynamic parameters achieved by lidocaine with clonidine or epinephrine, administered for maxillary infiltration anaesthesia, were studied in 40 patients (American Society of Anesthesiologists, physical status 1) who underwent upper third molar surgery. All patients received 2 ml of 2% lidocaine with clonidine (15 microg/ml; n=20) or epinephrine (12.5 microg/ml; n=20) in a randomized, double-blind fashion. Vascular effects were evaluated on the isolated human infraorbital arteries. The parameters of maxillary infiltration anaesthsia produced by a combination of lidocaine+clonidine were similar to those obtained with lidocaine+epinephrine. In both groups, haemodynamic parameters exhibited similar variations, with the exception of a significant reduction in heart rate and systolic blood pressure in the lidocaine+clonidine group and significant increase in heart rate in the lidocaine+epinephrine group, 10 min after surgery. Clonidine (10(-7), 10(-6) and 10(-5)M) produced an endothelium-independent vasocontractile effect on the isolated human infraorbital arteries. The results of this study indicate for the first time in dental anaesthesia that the lidocaine+clonidine combination could be a useful and safe alternative to lidocaine+epinephrine for intraoral infiltration anaesthesia.