Local laser targeted delivery of a platelet aggregating agent to occlude retinal and choroidal vessels was evaluated in rabbits and rats. Liposomes containing adenosine diphosphate (ADP) were administered intravenously and an argon laser was used to lyse the liposomes in main retinal arteries. Control vessels were treated with the same energy of laser without administering ADP. Fluorescein angiography performed 2 weeks later showed that all the control vessels were perfused. Ninety percent of the ADP-treated arteries showed complete or partial occlusion. Successful occlusion increased with the laser energy and decreased with increasing vessel diameter. Histopathology showed that occlusion was achieved in retinal as well as choroidal vessels. The inner retina remained relatively unaffected at the treatment site but the outer retina was thermally damaged. These preliminary results suggest that targeted delivery of a platelet aggregating agent holds promise for occluding vessels in the fundus.