Our purpose was to compare incidence of post-surgical pain associated to the endodontic therapy where the instrumentation on the root canal was performed by the method of Marshall & Pappin and the method of Marshall & Pappin complemented by the ultrasonic. Seventy patients with only one tooth needing endodontic treatment were treated by one of the methods and, posteriorly, evaluated. The endodontic treatment was performed at one time and from the seventy teeth, thirty have been instrumented by the manual method complemented by the ultrasonic and forty by the manual instrumentation. The patients were clinically controlled after the endodontic treatment was finished during periods of 24, 48 and 72 hours to evaluate their post-surgical condition. The results suggest that were no statistically significant differences (p less than 0.05) in the incidence of pain between the employed methods or according to the pulpar semiologic condition in any of the observed periods. However, we have realized that there was a tendency for a smaller percentage of a postoperative pain in those cases of necropulpectamy treated by the endosonic ultrasonic synergistic system. In those cases of biopulpectomy this has been not observed.