Purpose: To evaluate the additive ocular hypotensive effect of latanoprost and dorzolamide in combination, on intraocular pressure reduction in patients with elevated intraocular pressure (IOP). Methods: Thirty patients with ocular hypertension or early capsular or primary open-angle glaucoma and elevated IOP were randomly assigned to two parallel treatment groups. The treatment period was twenty days. Fifteen patients (Group 1) received latanoprost once daily during the first ten days and, in addition, dorzolamide three times daily during the second ten days. Fifteen patients (Group 2) received dorzolamide three times daily during the first ten days and, in addition latanoprost, once daily during the second ten days. IOP was measured and conjunctival hyperemia was evaluated. Results: In Group 1, the mean IOP on day 0 was 26.8 mmHg; on day 10, 18.7 mmHg; and on day 20, 15.9 mmHg. In Group 2, the mean IOP on day 0 was 26.3 mmHg; on day 10, 21.2 mmHg; and on day 20, 16.1 mmHg. Both groups had clinically significant IOP-lowering effect on day 10 as compared with baseline day (30.2% and 19.4% respectively) (p < 0.01). When dorzolamide was added to latanoprost, the additional IOP reduction was 2.8 mmHg (15%) (p < 0.01) compared with 5.1 mmHg (24.1%) (p < 0.01) when latanoprost was added to dorzolamide. No local serious adverse reactions were observed. A mild but statistically significant increase in conjunctival hyperemia was seen in latanoprost applied patients. Conclusions: The results showed that latanoprost and dorzolamide can be combined successfully to reduce IOP with their additive effects.