Objective To study the changes of the four active substances endothelin(ET),calcitonin gene related peptide (CGRP), thromboxane B2 (TXB2) and 6-Keto-prostaglandin F1? (6-Keto-PGF1?) in plasma when they acted on . each other in the formation and development of diabetic retinopathy. Methods Using the method of radio-immunity,the levels of ET,CGRP,TXB2, 6-Keto-PGF,. in plasma were measured in four groups of patients with type 2 diabetes (group 1: 40 cases without retinopathy; group 2: 40 cases with primary retinopathylgroup 3. 40 cases with hyperplasia type of retinopath; group 4: 40 cases normal controls). Results The results showed that ET increased progressively (P