PURPOSE: To investigate the efficacy and dose-response relationship of three concentrations (0.2%, 0.7%, and 2.0%) of dorzolamide hydrochloride in lowering elevated intraocular pressure (lOP) in patients during a six-week period and to evaluate the efficacy of 0.7% and 2.0% dorzolamide administered for an additional year. METHODS: This prospective, double-masked, randomized, placebo-controlled, multinational study enrolled 333 adults with open-angle glaucoma or ocular hypertension. During the six-week dose-response phase, patients were randomized to thrice-daily dosing of four treatments: 0.2%, 0.7%, or 2.0% dorzolamide or placebo (vehicle of dorzolamide). During a one-year extension, patients received 0.7% or 2.0% dorzolamide, and, if needed, 0.5% timolol twice daily for elevated IOP. RESULTS: In the dose-response phase, mean percent reduction of IOP (peak) was 16% to 18% for 2.0% and 0.7% dorzolamide and 4% to 7% for the placebo group, for a net reduction of IOP by dorzolamide of 11% to 14%. The 0.2% concentration of dorzolamide was not sufficiently active for further consideration. During the extension, dorzolamide maintained an adequate reduction of lOP in 55% (174 of 316) of patients. Throughout the study, the reduction in IOP was numerically greater for patients receiving 2.0% vs 0.7% dorzolamide. After 12 months of receiving dorzolamide, 20% to 28% of total carbonic anhydrase activity was observed. CONCLUSIONS: Topical dorzolamide used three times daily in concentrations of 0.7% or 2.0% lowered lOP and was generally well tolerated as monotherapy or in combination with 0.5% timolol.