The effect of adding hyaluronidase to regional ophthalmic anaesthesia with etidocaine 1.5% was examined. Two studies were performed in a double-blind fashion. In Study #1, 70 patients were given peribulbar anaesthesia with etidocaine either with or without hyaluronidase (7.5 IU.ml-1) using a standard intraorbital injection and separate lid injections. The block was supplemented as needed. Lower intraorbital volumes (6.4 +/- 2.2 ml vs 8.2 +/- 2.3 ml, P < 0.01) and improved scores for globe akinesia (P < 0.01), lid akinesia (P < 0.01) and analgesia (P < 0.05) were recorded in the hyaluronidase group than in the plain etidocaine group. In Study #2, 80 patients were randomized to receive etidocaine and hyaluronidase either at a concentration of 7.5 IU.ml-1 or 15 IU.ml-1 using a two-injection-site technique. No differences were noted in the volumes of local anaesthetics required or in the success rates between the two groups. It was concluded that the addition of hyaluronidase to etidocaine decreases the volume needed and improves the quality of block compared with plain etidocaine. Doubling the dose of hyaluronidase does not improve the effectiveness of block.