The effects of increasing the maximum prescribed volume of 50 ml lidocaine 1% to 65 ml in a combined sciatic 3-in-1 block were investigated in 25 adult patients. The goal of the study was (1) to show possible increase in the success rate and (2) to determine if toxic plasma levels of local anaesthetic would be reached. Further more, we wanted to find out if there were any side-effects. The patients were divided into three groups according to body weight: group I, 50-69 kg (n = 7); group II, 70-80 kg (n = 9); group III, over 80 kg (n = 9). Besides clinical observation, the plasma levels of local-anaesthetic were determined over a 90-min period. RESULTS. Following the neural blockade, the obturator nerve was the first to be rendered insensitive after 4.8 +/- 3.6 min, followed by the saphenous (7.2 +/- 4.4 min) and femoral nerves, and finally by the lateral femoral cutaneous nerve after 12.5 +/- 5.3 min. Around the knees, the motor blockade was complete after 11.9 + 4.3 min and around the hips 11.2 +/- 4.6 min. Intraoperatively, one of these 25 patients needed an additional general anaesthetic, as he did not tolerate the Esmarch cuff. The postoperative analgesia in 24 patients lasted 268 +/- 55 min; the patient who had a general anaesthetic in addition had a postoperative analgesia of 315 min. Group I showed levels of mean 2.04 +/- 0.64 microns/ml, group II 1.84 +/- 0.38 microns/ml and group III 1.69 +/- 0.63 microns/ml. There were no statistical differences between the three groups. CONCLUSION. Increasing the dosage of lidocaine from 500 to 650 mg makes the block very successful without any toxic side-effects.