Perivascular axillary blockade was performed on 90 patients with the aid of a catheter technique. The patients were randomly allocated to receive either 40, 50 or 60 ml of 1 % mepivacaine with adrenaline 1:200,000. Blood concentrations of mepivacaine were measured up to 90 min after injection in seven, eight and ten of the patients from the three groups. Sensory and motor blockade was evaluated 20, 30 and 40 min after injection. All groups showed the same temporal development of the blockade, i.e. improval of the blockade during the period from 20 to 40 min after injection, but no difference was found in the sensory or motor blockade between the three groups. However, a further analysis of the incomplete blockades showed a better quality of the sensory blockade in the groups given 50 and 60 ml than in the group given 40 ml. None of the 90 patients showed any signs of systemic toxic reactions. The mean peak values of blood concentrations were 0.5-1.0 μg/ml higher in the groups A given 50 ml and 60 ml than in the group given 40 ml. On the basis of the present and two previous investigations on the dose response in perivascular axillary blockade, a dose of 50 ml 1% mepivacaine with adrenaline or I r another equivalent drug with vasoconstrictor is recommended.