OBJECTIVE:To investigate relationship between plasma endotbelin(ET)and serum angiotensin converting enzyme (ACE)levels and diabetic retinopathy (DR). METHODS: Plasma ET and serum ACE levels were measured in 62 patients with diabetes mellitus(DM) and in 30 normal control subjects with radioimmunoassay and ultraviolet-spectrophotometry. RESULTS:Plasma ET and serum ACE levels in patients with DR were significantly higher than in patients without DR (P＜0.01). Along with the progression of DR,plasma ET levels were significantly elevated and serum ACE levels were gradually elevated. CONCLUSIONS :These findings suggest that increased plasma ET and serum ACE levels may be related to the development and progression of DR. （Chin J Ocul Fundus Dis,1996,12: 177-179）