Moxisylyte hydrochloride (α<sub>1</sub>-blocker) selectively vasodilates cerebral vessels without reducing blood pressure. We investigated the effect of the drug on retinal circulation in 15 patients (17 eyes) with diabetes mellitus, using the video-densitometric image analysis of fiuorescein angiography. We compared the build-up time (BT), the time constant of washout rate (TC) and the mean circulation time (MCT) before and after oral therapy with moxisylyte. In 16 eyes, BT was shortened significantly and MCT was only slightly shortened 1 h after oral therapy with moxisylyte. After 2 weeks of daily administration, MCT was shortened and TC of the artery was increased significantly in 6 eyes. Since retinal circulation in patients with diabetes mellitus was improved by moxisylyte, the drug may be useful to treat ocular disorders such as diabetic retinopathy.