The purpose of this study was to evaluate the success rate ofmonotherapy with latanoprost 0.005% once daily versus brimonidine 0.2% twice daily in patients with open-angle glaucoma or ocular hypertension. Patients who were prescribed latanoprost or brimonidine as monotherapy were included in this study, and their consecutive charts were retrospectively reviewed. The primary efficacy variable was success of therapy, defined as a reduction in intraocular pressure > or =3 mm Hg without an adverse event leading to discontinuation over a potential of six months of therapy. We included 157 patients in this study. In the latanoprost group, 64 of 92 (70%) were considered successes; 26 of 65 (40%) were successful with brimonidine (P < 0.001). Nine failed brimonidine therapy, and one latanoprost, because of an adverse event, and the rest failed because of inadequate intraocular pressure response. The change from baseline in intraocular pressure was significantly greater with latanoprost (mean +/- S.D., 21.6 +/- 5.1 to 17.1 +/- 3.3 mm Hg) than brimonidine (23.7 +/- 5.6 to 21.9 +/- 5.7 mm Hg) (P = 0.001). Overall, 52 (80%) brimonidine- and 41 (45%) latanoprost-treated patients required additional visit(s) to adjust therapy to further lower intraocular pressure or to assess an adverse event (P < 0.001). In conclusion, latanoprost more likely provides a successful response to therapy than brimonidine when used as monotherapy in primary open-angle glaucoma or ocular hypertensive patients.