Two independent, prospective trials were recently conducted to assess the efficacy of latanoprost in reducing intraocular pressure (IOP) in patients with primary angle-closure glaucoma (PACG). The first study was a 2-week, randomized, double-masked comparison of latanoprost treatment and timolol treatment in patients with PACG. Patients were randomized to one of two parallel treatment groups, receiving either placebo in the morning and latanoprost 0.005% in the evening, or timolol 0.5% twice daily. The mean IOP reduction in latanoprost group was 8.8 +/- 1.1 mm Hg (mean +/- SEM, p < 0.001; 34.2%) from a mean baseline IOP of 25.7 +/- 0.9 mm Hg, and the corresponding figures for the timolol group were 5.7 +/- 0.9 mm Hg (p < 0.001; 22.6%) from a mean baseline IOP of 25.2 +/- 1.1 mm Hg. A significantly greater IOP reduction of 3.1 +/- 1.5 mm Hg (95% confidence interval: 0.1 to 6.0) was achieved in the latanoprost group compared to the timolol treatment group (p = 0.04). In the second study, latanoprost 0.005% once a day was added adjunctively to PACG patients with persistently elevated IOP after iridectomy, despite treatment with beta-blockers and pilocarpine. The IOP decreased by about 21% during the first 3 months, and showed a reduction of about 36% at the end of 1 year. At the 1-year follow-up, IOP was <20 mm Hg in all eyes. In both studies, latanoprost was well tolerated with few adverse events. These results demonstrate that latanoprost is effective in reducing IOP in patients with PACG.