We evaluated the ocular hypotensive effect and safety of a synthetic prostamide analogue; bimatoprost 0. 03% (Lumigan , Allergan, Inc.), in Taiwanese patients with glaucoma or ocular hypertension unable to achieve target intraocular pressure (IOP) using a prostaglandin analogue prodrug, latanoprost 0.005%. Methods: This open-label, one-arm, nonrandomized, phase IV study recruited 47 Chinese adults with ocular hypertension or glaucoma who were treated with latanoprost and whose IOP was ≧18 mmHg. IOP, visual acuity, slit lamp biomicroscopy, vital signs, and adverse events were recorded at baseline, and at weeks 2, 4, and 12 of therapy. During treatment, latanoprost therapy was discontinued and one drop of bimatoprost was instilled every evening in the affected eye or eyes. The main outcome measures were the mean change in IOP and the percentage of patients achieving the target IOP (< 18 mmHg). Results: Compared with baseline IOP, after bimatoprost therapy, the mean change in IOP was -3.1 mmHg after two weeks and -3.3mm Hg after 12 weeks of treatment. About 58% of patients achieved the target IOP of 18 mmHg or less. Twenty-one patients reported one or more adverse event; 19 of these had adverse events that were possibly or probably drug related. Eye pruritus (14.9%) and conjunctival hyperemia (14.9%) were reported most frequently. Conjunctival hyperemia (42.6% at baseline and 38.3% at week 12) was the most common biomicroscopic finding. Conclusions: Bimatoprost is well tolerated and significantly decreases IOP in Taiwanese patients whose glaucoma or ocular hypertension is uncontrolled by latanoprost.