['Vascular endothelial growth factor (VEGF) is thought to be instrumental in the progression of diabetic retinopathy. Indications exist that the renin-angiotensin system is involved in VEGF overexpression. We assessed the vitreous VEGF concentrations in patients and related them to anti-hypertensive treatment, with special interest in the use of ACE-inhibitors.', 'Samples of vitreous fluid (10-80 microl) were obtained from 39 patients both with Type I (insulin-dependent) and Type II (non-insulin-dependent) diabetes mellitus and 11 non-diabetic patients undergoing intra-ocular surgery. The VEGF-A concentrations were assessed by immunoassay.', 'Control patients and patients without proliferative diabetic retinopathy ( n = 8) had low and comparable VEGF concentrations (medians < 50 pg/ml). In contrast, patients with proliferative diabetic retinopathy ( n = 31) had high vitreous VEGF concentrations (median 1134 pg/ml), which showed a negative correlation with the use of ACE inhibiting medication (Spearman rank-R = - 0.54; p = 0.002, n = 13). Diastolic and systolic blood pressure did not differ significantly between the two subgroups with proliferative diabetic retinopathy, i. e. those patients receiving ACE-inhibition (medians 88/160 mm Hg, respectively) and the others (90/160). For the mostly used ACE-inhibitor in the proliferative diabetic retinopathy group, i. e. enalapril ( n = 8), a linear dose-effect relation was observed (-20 +/- 4 pg x ml(-1) x mg(-1) x day(-1); p = 0.024; coefficient +/- SEM).'] Is angiotensin converting enzyme inhibiting therapy associated with lower vitreous vascular endothelial growth factor concentrations in patients with proliferative diabetic retinopathy?