AIM: To investigate the effect of hydralazine on choroidal blood flow in rabbits and laser-induced choroidal neovascularization (CNV) in rats and on tube formation of human umbilical vein endothelial cells (HUVEC). METHODS: Female New Zealand white rabbits were used with raised intraocular pressure (IOP) of the left eye to 40mmHg. Hydralazine (10g/L) eye drops were instilled and ocular blood flow was measured with colored microspheres technique. Male Brown Norway rats were treated with Nd:YAG laser to break Bruch's membrane. Hydralazine (5, 10, 20g/L) eye drops or saline alone was instilled three times a day for 4 weeks after laser treatment. Fluorescein angiography (FA) and choroidal flat mount were used to measure the area of CNV. Tube formation of HUVEC was studied at different concentrations of hydralazine. RESULTS: With raised IOP to 40mmHg on rabbits, 10g/L hydralazine eye drops enhanced the choroidal blood flow significantly at 30 and 60 minutes after drug instillation. After 4 weeks of drug treatment, 5, 10 and 20g/L hydralazine eye drops all reduced the CNV formation dramatically measured by fluorescein angiography and choroidal flat mount. When HUVEC was cultured on matrix gel for 48 hours, the tube formation of HUVEC were prevented.by hydralazine at 3-30mg /L. CONCLUSION: Hydralazine prevents CNV formation in vivo and HUVEC tube formation in vitro, and enhances rabbits' choroidal blood flow after ischemia. It is hoped that hydralazine could be used to treat age-related macular degeneration in the future.