The quality of anaesthesia provided by three dosages of prilocaine, 40 ml 0.5%, 20 ml 1%, or 40 ml 1%, administered in random order, for intravenous regional anaesthesia of the lower extremity below the knee was compared in six volunteers. Limited sensory blockade was achieved in the groups with 40 ml 0.5% and 20 ml 1% during the 30-minute test period. One subject was not fully anaesthetised with any of the dosages used. Recovery was rapid (mean 12-13 minutes) in these two groups. In two subjects given 40 ml of 1%, complete recovery took 90 minutes. At 30 minutes, the degree of flexion remaining in the great toe (control 100%) was 4% in the groups who received 40 ml of 0.5% and 1%, but 34% in those who received 20 ml of 1% respectively. Full motor recovery was achieved in 8-9 minutes. Five of six volunteers who received the 400-mg dose experienced subjective signs of central nervous system side effects when the cuff was released. In this group, the mean plasma level of prilocaine at 2 minutes was 1.22 micrograms/ml, maximum 2.12 micrograms/ml. In a radiological examination, no leak of contrast medium under the tourniquet cuff (300 mmHg) was detected. The development of anaesthesia was fastest following the largest dose, but the large number of central side effects makes that dosage less suitable for clinical work.