Purpose. To compare the effects of dorzolamide-timolol combination and brimonidine on intraocular pressure (IOP) after phacoemulsification surgery. Methods. This prospective, randomized study included 69 eyes of 43 patients undergoing phacoemulsification and foldable intraocular lens implantation. Twenty-one patients were women and 22 were men. The mean patient age was 69.7 +/- 12.4 years. Patients were randomly assigned to one of three treatment groups preoperatively. Group A (n = 23) received one drop of dorzolamide-timolol fixed combination and group B (n = 23) received one drop of brimonidine tartrate 0.2% immediately after surgery. In group C (n = 23), patients received no treatment and served as a control group. IOP was measured by Goldmann applanation tonometry 6 hours and 24 hours after surgery. Results. Six hours after Surgery, the mean IOP was significantly lower in group A (16.3 +/- 2.9 mm Hg) than in groups B (20.6 +/- 2.9 mm Hg) and C (24.6 +/- 5.4 mm Hg). However, 24 hours after surgery, the mean IOP was higher in group C (19.8 +/- 4.7 mm Hg) than in the other two groups (14.1 +/- 2.8 mm Hg in group A and 17.5 +/- 2.7 mm Hg in group B). Conclusions. Prophylactic treatment with dorzolamide-timolol fixed combination was more effective than brimonidine in reducing IOP 6 hours and 24 hours after phacoemulsification surgery.