The purpose of this study was to assess the efficacy of latanoprost 0.005% and timolol maleate 0.5% in black and white patients with elevated intraocular pressure (IOP). This double-masked, randomized, 2-period crossover study included 39 eyes in 22 patients with primary open-angle glaucoma or ocular hypertension. After a 2- to 4-week washout period, patients were randomly assigned to receive either vehicle placebo in the morning and latanoprost in the evening or timolol maleate twice daily for 6 weeks. Then, after a 4-week washout period, patients received the opposing treatment for 6 weeks. Both latanoprost and timolol maleate significantly lowered IOP from baseline in both black and white patients. Latanoprost treatment was associated with lower mean IOP compared with timolol treatment in black patients (P=.013 at 8am,P=.1 9 at 10am). At 10am at the end of the treatment period, the mean±SD change from baseline IOP in black patients receiving latanoprost was significantly greater than that of white patients (−10.2±7.0 and −5.9±2.5 mm Hg, respectively; P=.042). The mean±SD change from baseline IOPs in black patients was not significantly different from that in white patients at 8am at the end of the treatment period for the latanoprost group and at 8am and 10am at the end of the treatment period for the timolol maleate group. In white patients, the change from baseline IOP in light (grade 1) irises was not significantly different from dark (grade 5) irises after treatment with either latanoprost or timolol maleate. In summary, intraocular pressure after treatment with latanoprost was lower than that after timolol treatment in black patients with primary open-angle glaucoma or ocular hypertension, and at 1 of 2 timepoints, latanoprost caused a significantly greater reduction of IOP in black patients than in white patients.