Blood loss in periodontal flap surgery using lidocaine 2% with either 1:50,000 or 1:100,000 epinephrine was compared. Ten patients from the graduate periodontal clinic were selected for the study. After the initial therapy which included oral hygiene instruction, scaling and root planning and occlusal adjustment, 20 surgical procedures were performed. In any one patient if 1:50,000 epinephrine was used on the posterior sextant of an arch, then 1:100,000 epinephrine was used on the contralateral side, with similar volumes being injected by the same method. Blood loss was determined by the cyanmethemoglobin comparison technique. Procedures using lidocaine 2% with 1:100,000 epinephrine generally had more than twice as much blood loss as those using lidocaine 2% with 1:50,000 epinephrine.