The effect of supplementing a standardised local anaesthetic mixture with hyaluronidase was studied in 60 patients undergoing peribulbar block for intra-ocular surgery. All the patients had the block performed with a 2:1 mixture of lignocaine 2% and bupivacaine 0.75%, but in half of the cases hyaluronidase 50 u.ml-1 was added to the solution by random allocation. The mean volumes of solution injected were 8.9 and 9.0 ml in the control and hyaluronidase groups respectively. Five minutes after injection the block was deemed unsuccessful in one third of the patients in each group and these patients required supplementary injections. At 15 min all but one patient in each group had satisfactory block and these two patients subsequently required retrobulbar block. There were no statistically significant differences between the two solutions in rate of onset of block, requirement for supplementation, block failure, or surgical conditions. There were no significant complications. We conclude that the addition of hyaluronidase 50 u.ml-1 to the local anaesthetic mixture described confers no advantage at the volumes of local anaesthetic used.