The onset of akinesia of the extraocular muscles was assessed after peribulbar block with a plain or pH-adjusted solution of 0.75% bupivacaine and hyaluronidase. Thirty-five patients were randomly assigned to receive either 0.75% bupivacaine with hyaluronidase 15 units/ml (pH 5.45 +/- 0.12) or the same pH-adjusted solution (0.15 mEq sodium bicarbonate per 30 ml of 0.75% bupivacaine to give a final pH of 6.82 +/- 0.09) in a double-blind, prospective manner. Onset of akinesia was determined to the nearest minute. Supplemental injections were given after 20 min in the event of incomplete akinesia. The group receiving pH-adjusted bupivacaine had a statistically faster onset time for complete akinesia than did the control group (5.3 +/- 1.2 min vs. 14.3 +/- 2.3 min, respectively; P less than 0.001). Five of 17 patients in the control group required a supplemental injection, whereas only one of 17 patients in the treatment group had a supplemental block at 20 min (P less than 0.05). Thus, pH adjustment of a solution of bupivacaine and hyaluronidase with sodium bicarbonate hastens the onset time and improves the initial success rate of peribulbar block.