Purpose. Viscoelastic-induced ocular hypertension following penetrating keratoplasty (PK) may result in endothelial cell loss and optic nerve damage. Methods: In a prospective, randomized, masked trial, two doses of oral sustained-release acetazolamide were compared to a single dose of topical 0.5% timolol gel after 40 PKs. Results:: The mean preoperative intraocular pressure (IOP) was 17.4 mm Hg for the oral acetazolamide group and 16.7 mm Hg for the timolol gel group. The mean IOP on the first postoperative day was 17.9 mm Hg with oral acetazolamide and 12.9 mm Hg with timolol gel. One patient developed significant adverse reactions with oral acetazolamide: there were no adverse reactions with timolol gel. Conclusion: Prophylactic use of timolol gel for viscoelastic-induced ocular hypertension after PK appears to offer better IOP control than oral acetazolamide, with potentially fewer adverse systemic effects