PURPOSE: To compare emedastine ophthalmic solution 0.05% BID to levocabastine ophthalmic suspension 0.05% BID in reducing chemosis, eyelid swelling and other signs and symptoms in subjects with seasonal allergic conjunctivitis. METHODS: In a randomized, double-masked, parallel controlled study, emedastine ophthalmic solution 0.05% BID was compared to levocabastine ophthalmic suspension 0.05% BID for control of chemosis, eyelid swelling and other parameters in the environmental allergy study model. RESULTS: At Days 7, 14, 30 and 42, emedastine was significantly better than levocabastine at controlling chemosis and eyelid swelling (p < 0.05). A statistical trend was seen at Day 3 (0.05 < p < 0.10). Results were clinically relevant at Days 30 and 42. Emedastine was also significantly better at reducing redness and itching at Days 7, 14, 30 and 42 (p < 0.05). CONCLUSION: Emedastine is more efficacious than levocabastine in reducing chemosis, eyelid swelling and other efficacy variables associated with seasonal allergic conjunctivitis.