The object of this study was to compare the long term efficacy and safety of bimatoprost with timolol in patients with glaucoma or ocular hypertension. In a 12-month extension of two identically-designed 1-year, multicenter, randomized, double-masked clinical trials, patients were treated topically with bimatoprost 0.03% QD (n = 167), bimatoprost 0.03% BID (n = 131), or timolol 0.5% BID (n = 81). Main Outcome measures were IOP at 8 AM and 10 Am and safety parameters. Bimatoprost QD provided significantly greater mean reduction from baseline IOP than did timolol at both measurements at each Study Visit (P less than or equal to .001). At 10 AM (peak timolol effect) at month 24, the mean reduction from baseline IOP was 7.8 mm Hg with bimatoprost QD and 4.6 mm Hg with timolol (P < .001). Patients treated with bimatoprost QD also sustained significantly lower mean TOP than timolol-treated patients at every follow-up visit throughout the 2-year study period (P less than or equal to .006). At 10 AM at month 24, a significantly greater proportion of bituatoprost QD than tirriolol patients achieved target pressures of less than or equal to 13-18 min Hg (P less than or equal to .010). Bimatoprost sustained an excellent safety profile during the second year of treatment. Most adverse events were mild, and there were no reports of increased iris pigmentation, uveitis, or CME. The incidence of hyperemia was significantly higher with bimatoprost QD (13.8%) than with timolol (2.5%) (P=.006). Mean reduction from baseline IOP with bimatoprost BID was not significantly different from that with timolol at month 24 at 10 AM (P=.474). We conclude that bimatoprost QD provides superior IOP lowering to timolol, and is safe and well tolerated over 24 months of treatment. (SurvOphthalmol49(Suppll):S4E,-S52,2004. (C) 2004 Elsevier Inc. All rights reserved.).