Abstract The value of Bier blocks for the manipulation of fractures and for operations on the upper limb is well recognized. Two anaesthetic agents, bupivacaine and prilocaine, are widely used for this purpose. A prospective double blind trial of 200 patients has been carried out to compare the efficacy of each drug and the incidence of side effects. The study shows that bupivacaine was associated with a greater number of successful fracture reductions than prilocaine with little difference in their analgesic effects, but this was balanced by more minor side effects with bupivacaine. There was little difference in the time from injection to analgesia in the two groups. All intravenous regional analgesia procedures were carried out by junior orthopaedic or accident and emergency doctors. The overall success rate for analgesia was 91 per cent but marked cuff discomfort occurred in 9 per cent of patients. There was a clear association between failure of analgesia and two of the doctors carrying out the procedure.