Visual loss from diabetic retinopathy occurs primarily from complications of either abnormal new vessel growth (proliferative diabetic retinopathy, PDR) or increased retinal vascular leakage (diabetic macular edema, DME). We have previously shown that vascular endothelial growth factor (VEGF) is a major mediator of these complications and that VEGF effects are mediated through activation of PKC-Beta. Inhibitors of VEGF and PKC-Beta are entering clinical trials for the treatment of PDR and DME. Both VEGF and PKC-Beta have also been implicated in the progression of early stages of diabetic retinopathy. To date, assessment of VEGF in patients has been limited due to either the need to obtain intraocular fluid samples or inadequate sensitivity of blood assays. The PI has developed a highly sensitive VEGF ELIZA which can readily detect the low basal levels of VEGF in both blood and urine. Preliminary data suggest that peripheral VEGF concentration may reflect retinopathy status and are effected by various physiologic processes. If VEGF in the blood or serum correlate with retinopathy level then measurement of VEGF from these peripheral fluids might be useful in identifying patients at risk of developing PDR or DME and might help in monitoring responses to anti-VEGF therapies. In addition, we have collaboratively developed techniques to specifically measure activated PKC-Beta in human monocytes. Thus, the specific aims: 1) Determine the correlation between peripheral VEGF, ocular VEGF and diabetic retinopathy in a cross- sectional clinical study; 2) Determine the correlation between activated PKC-Beta in monocytes and diabetic retinopathy in a cross- sectional clinical study; 3) Determine the role of VEGF in the progression of diabetic retinopathy in a prospective clinical study and 4) Evaluate novel VEGF antibodies now available for the VEGF assay. The cross-sectional studies will evaluate 200 patients with type 1 diabetes and no proteinuria. Retinopathy level will be assessed from stereoscopic fundus photographs. These studies will provide the first rigorous evaluation of serum and urine VEGF, activated PKC-Beta and diabetic retinopathy. The prospective study will evaluate VEGF in plasma samples obtained from patients in the EUCLID study which is a continuing randomized, placebo-controlled trial of the ACE inhibitor lisinopril in a well characterized cohort of 530 normotensive patients with normo- or microalbuminuria and two years follow-up. Retinopathy level and progression have been documented. These studies will provide the first prospective evaluation of plasma VEGF and its correlation with retinopathy progression and onset of microalbuminuria.