PURPOSE: To compare the ocular hypotensive efficacy and safety of a fixed-dose combination (FDC) of the Rho kinase inhibitor netarsudil and latanoprost vs monotherapy with netarsudil or latanoprost. DESIGN: Three-month primary endpoint analysis of a randomized, double-masked, phase 3 clinical trial. METHODS: Adults with open-angle glaucoma or ocular hypertension (unmedicated intraocular pressure [IOP] >20 and <36 mm Hg at 8:00 AM) were randomized to receive once-daily netarsudil/latanoprost FDC, netarsudil 0.02%, or latanoprost 0.005% for up to 12 months. The primary efficacy endpoint was mean IOP at 8:00 AM, 10:00 AM, and 4:00 PM at week 2, week 6, and month 3. RESULTS: Mean treated IOP ranged from 14.8-16.2 mm Hg for netarsudil/latanoprost FDC, 17.2-19.0 mm Hg for netarsudil, and 16.7-17.8 mm Hg for latanoprost. Netarsudil/latanoprost FDC met the criteria for superiority to each active component at all 9 time points (all P < .0001), lowering IOP by an additional 1.8-3.0 mm Hg vs netarsudil and an additional 1.3-2.5 mm Hg vs latanoprost. At month 3, the proportion of patients achieving mean diurnal IOP ≤15 mm Hg was 43.5% for netarsudil/latanoprost FDC, 22.7% for netarsudil, and 24.7% for latanoprost. No treatment-related serious adverse events were reported; treatment-related systemic adverse events were minimal. The most frequent ocular adverse event was conjunctival hyperemia (netarsudil/latanoprost FDC, 53.4%; netarsudil, 41.0%; latanoprost, 14.0%), which led to treatment discontinuation in 7.1% (netarsudil/latanoprost FDC), 4.9% (netarsudil), and 0% (latanoprost) of patients. CONCLUSIONS: Once-daily netarsudil/latanoprost FDC demonstrated IOP reductions that were statistically and clinically superior to netarsudil and latanoprost across all 9 time points through month 3, with acceptable ocular safety.