Doppler ultrasound was used to detect possible flow changes in the carotid arteries of patients with central retinal artery and vein occlusion. Twenty-three patients with central retinal artery occlusion (mean age 56, SD 11, years) were examined 4 to 48 months after the development of the occlusion and compared with age and sex matched control subjects with no history of any disease known to be associated with pathological changes in carotid vessels. Significant stenosis or occlusion of one or more carotid arteries was discovered in eight patients with retinal artery occlusion, while the ultrasonic findings were normal in all the controls (p less than 0.005). Blood flow was evaluated by the same method in 16 patients with central retinal vein occlusion (mean age 57, SD 9, years) six to 48 months after the event. A control group was chosen according to the same criteria as in previous comparison. Pathological ultrasonic findings were observed neither in the patients with retinal vein occlusion nor in the control group. The results suggested a possible aetiological relation between pathological changes in the carotid arteries and occlusion of the central retinal artery, but not occlusion of the central retinal vein.