This prospective study was done to compare the efficacy of timolol and acetazolamide in lowering the intraocular pressure (IOP) secondary to the use of sodium hyaluronate (Healon) in cataract surgery. Fifty patients undergoing extracapsular cataract extraction and implantation of a posterior chamber lens were randomly assigned to one of four treatment groups: no viscoelastic (10 patients), Healon with 0.5% timolol drops postoperatively (12 patients), Healon with acetazolamide postoperatively (16 patients), or Healon only (12 patients). The IOP was measured during the first 24 hours after surgery. Sodium hyaluronate caused a marked increase in IOP in the early (6 to 12 hours) postoperative period. Timolol proved to be more effective than acetazolamide in controlling this pressure increase.