We investigated the ocular hypotensive effect and possible adverse reactions of a new timolol maleate formula, WP-934 ophthalmic solution, which is timolol maleate solution dissolved in a reversible thermo-setting gel. Once-daily instillation of 0.25 or 0.5% WP-934 ophthalmic solution was administered in a prospective, randomized manner at 29 institutions for 8 weeks to patients with primary open-angle glaucoma or ocular hypertension, and for another 16 weeks in a limited number of these patients. Patients were closely monitored throughout the study by ophthalmic and systemic examinations, and by continuous evaluation of symptoms. The new timolol formula demonstrated a significant ocular hypotensive effect throughout the study period. Adverse effects were minor. WP-934 ophthalmic solution, timolol maleate dissolved in a reversible thermo-setting gel, has a significant ocular hypotensive effect in eyes with primary open-angle glaucoma and ocular hypertension.