Brimonidine tartrate is a relatively selective alpha2-agonist that effectively reduces mean intraocular pressure (IOP) and the incidence of IOP spikes after laser trabeculoplasty. The authors were interested in evaluating the dose response of brimonidine when applied topically for a longer duration in patients with elevated IOPs.The authors conducted a 1-month, multicentered, double-masked, randomized, placebo-controlled, parallel clinical study in 194 patients with ocular hypertension or glaucoma (mean IOP, 25.6 +/- 3.2 mmHg). The authors administered three concentrations of brimonidine (0.08%, 0.2%, and 0.5%) or placebo bilaterally every 12 hours for 1 month. The authors evaluated the following parameters: IOP, heart rate, blood pressure, visual acuity, pupil size, basal tear secretion as well as patient comfort at baseline, day 1, week 1, week 3, and week 4.All concentrations of brimonidine significantly reduced IOP, compared to baseline and placebo, at all follow-up visits. Maximum mean IOP decreases from baseline of 20.8%, 27.2%, and 30.1% were observed for the 0.08%, 0.20%, and 0.5% treatment groups, respectively. On days 1 and 21, the 0.2% and 0.5% treatment groups exhibited significantly greater IOP decreases than did the 0.08% group. After the initial steep decline in IOP, the effect decreased slightly and stabilized at day 14 at the level that was maintained throughout the study. The most frequent side effects reported were fatigue and dry mouth. No significant changes in heart rate were reported. Statistically significant decreases in mean blood pressure without clinical symptoms were observed within the 0.2% and 0.5% treatment groups.Brimonidine 0.2% is well tolerated, efficacious, and shows potential as an agent in the long-term treatment of elevated IOP.