To explore the possible involvement of adrenomedullin (AM)in the pathophysiology of diabetic retinopathy, we employed streptozotocin (STZ)-induced diabetic rats to study the alteration of the AM expression in the retinal pigment epithelium (RPE) cells of diabetic and normal rats by immunohistochemistry. The weight, blood sugar and urine sugar were also measured before and after model induction in both groups. The data of weight, blood sugar and urine sugar indicated no significant difference between the two groups before animal model induction. Four weeks after the induction of diabetes,the differences between the control and the diabetic group in weight,blood sugar and urine sugar were distinct (P<0.01). When compared with the normal retina, a significant increase of AM expression was observed in the diabetic rat' RPE cells,as shown by increased optical density and immunohistochemistry positive cell number(P<0.01). Our study provides experimental evidence that up-regulation of AM expression in retina of streptozotocin-induced diabetic rats under hyperglycemia condition. Adrenomedullin may play a role in the pathophysiology of diabetic retinopathy.