Perivascular axillary blockade was performed on 233 patients with the aid of a catheter technique. All patients received a primary injection of 50 ml of mepivacaine 1% with adrenaline. Sensory blockade was evaluated 20, 30 and 40 min after injection, and a complete sensory blockade was found in 90 (39%), 131 (57%) and 146 (63%), respectively. The blockade effect of a supplementary perivascular injection of 20 ml of the same agent was investigated on the remaining 87 blockades, which could be divided into three categories: 1) blockades which at 20 min showed lack of analgesia in several cutaneous segments of the hand (34 patients); 2) blockades which at 30 min showed a total lack of sensory blockade within a limited area (29 patients); and 3) blockades which at 40 min showed signs of blockade of all cutaneous segments, but one or several segments were not blocked with an intensity compatible with surgery (24 patients). Blockades of categories 1 and 2 were at 20 and 30 min, respectively, randomly allocated to control or to perivascular supplementation groups, while blockades of category 3 all had supplementation at 40 min. Sensory blockade was reevaluated 10 and 20 min after group allocation, and it was found that perivascular supplementation had no significant effect on the sensory blockade in category 1 and 2, while 68% of the blockades in category 3 improved to a complete blockade. It was concluded that the effect of a supplementary perivascular dose of local anaesthetic could be judged as acceptable with regard to intensifying an insufficient sensory blockade, but that it was incapable of extending the blockade into areas which were totally unblocked after the primary injection. On the basis of a previous and the present investigation, we have suggested practical, simple guidelines which might help the anaesthetist in deciding on his course of action when faced with an inadequate axillary blockade.