Objective:To evaluate the effect of dorzolamide on theintraocular pressure (IOP), ocular pulse amplitude(OPA), systemic blood pressure and pulse rate in open-angle glaucoma patients using a beta-blocker and 2%pilocarpine combination and beta-blockermonotherapy. The secondary aim was to find out theeffect of dorzolamide on IOP and OPA in patients usingselective versus nonselective beta-blocker.Methods:Thirteen patients who had beta-blocker andpilocarpine combination (Group 1) and 15 patients whohad beta-blocker monotherapy (Group 2) wereenrollled. A randomly selected eye of bilaterallyaffected patients was included in the observer-blindedand parallel-group study. Baseline data consisted of 4day-time IOP, OPA, systemic blood pressure and pulserate measurements. Patients in Group 1 discontinuedpilocarpine and used beta-blocker-dorzolamidecombination and patients in Group 2 used dorzolamideas a second-line therapeutic agent with a beta-blocker.The same measurements were performed after 4 weeksand after 6 months in both groups.Results:  In Group 1 the baseline IOP was 18.9±2.2mmHg; after 4 weeks and 6 months no statisticallysignificant change was observed (17.6±2.3 and 17.8±3.2mmHg respectively, p>0.05). However in Group 2, astatistically significant IOP decrease from 22.5 ± 3.3mmHg to 18.0 ± 2.0 mmHg after 4 weeks (p<0.05) andto 18.4 ± 1.8 mmHg after 6 months (p<0.05) occurred.There were no changes in OPA, systemic bloodpressure and pulse rate in either  groups during thefollow-up period. The additive effect of dorzolamidewith selective and nonselective beta-blockers wasanalyzed using a cross-sectional study design of thedata obtained from 28 eyes. Twelve patients who usedselective beta-blocker and dorzolamide showed anincrease in IOP (from 18.4±2.3 to 19.3±1.9 mmHg,p>0.05) and a decrease in OPA (from 3.7±1.2 to 3.2±0.9mmHg, p>0.05) after 5 months, although these changeswere not statistically significant. The IOP was stableduring the same period (17.3±2.0 and 17.2±2.6 mmHg,p>0.05) but the OPA showed a slight, but not significantincrease (2.7±1.1 and 3.1± 1.5 mmHg, p>0.05) in sixteenpatients using nonselective beta-blocker anddorzolamide.Conclusion:  Dorzolamide is safe and effective whenused with beta-blockers but its interaction withselective and nonselective beta-blockers needs furtherinvestigation.Key Words: Intraocular pressure, ocular pulse amplitude,medical therapy, beta-blocker, dorzolamide, pilocarpine