OBJECTIVE To compare the ocular hypotensive activity and safety profile of long-acting 1% carteolol hydrochloride eye drops (long-acting formulation) to those of 1% carteolol hydrochloride eye drops(currently prescribed drug) for reduction of intraocular pressure. METHODS Patients with primary open-angle glaucoma or ocular hypertension (146 cases) were assigned randomly to the long-acting drug group (74 cases) and the currently-prescribed drug group (72 cases). Long-acting eye drops were instilled once a day in the morning (along with one drop of placebo at night), and currently-prescribed eye drops were instilled twice a day in the morning and at night. Eye drops were administered for 8 weeks. Intraocular pressure was monitored at 2, 4, and 8 weeks after the initiation of drug instillation for evaluation of equivalence. RESULTS Intraocular pressure was significantly reduced during the entire follow-up period in both groups. In the long-acting drug group, the reduction of intraocular pressure was--3.5 +/- 0.2,--4.3 +/- 0.2 and--4.6 +/- 0.3 mmHg at 2, 4, and 8 weeks, respectively (paired t test). In the currently-prescribed drug group, the reduction of intraocular pressure was--4.1 +/- 0.2,--4.4 +/- 0.3 and--4.6 +/- 0.2 mmHg at 2, 4, and 8 weeks(paired t test). The safety profile was similar in both groups, and the tolerance for the long-acting eye drops was as good as for the currently-prescribed eye drops. CONCLUSIONS Because the efficacy of both drugs was equivalent, with an identical safety profile, the long-acting eye drops seem to be an efficacious formulation for clinical use in Japanese glaucoma patients.