Purpose: Endothelial dysfunction (ED) is a common feature of Chronic Kidney Disease (CKD) and Diabetes Mellitus (DM), and is thought to underlie the increased cardiovascular risk of both conditions. However, while the association between coronary artery ED and DM has been evidenced in previous studies, no data are available about the relationship between CKD and coronary ED. Methods: 63 consecutive patients (mean age 60±10; 40 males), 25 of whom affected by Type II DM (mean age 62±10; 13 males) and 38 non diabetic subjects (mean age 59±11; 27 males), underwent, on the same day, transthoracic echocardiographic coronary flow reserve (CFR) evaluation during cold pressure test (CPT), to assess endothelium dependent vasodilation, and dipyridamole (Dip) infusion (0.84 mg/kg i.v. in 6 min), to evaluate endothelium independent vasodilation. Glomerular Filtration Rate (GFR), as an index of renal function, was estimated by serum creatinine values using Cockroft-Gault formula. All patients had no significant stenosis at coronary angiography performed within one month from enrolment. Results: Mean GFR was 90.27±26.98 ml/min in the whole population, 86.2±27.9 ml/min in DM patients and 92.94±26.39 ml/min in non DM patients (p=ns). Mean Dip-CFR (2.42±0.72 vs 2.84±0.73; p=0.028), as well as CPT-CFR (1.47±0.28 vs 1.65±0.29; p=0.02) were significantly lower in DM compared to non DM patients. In diabetic group, GFR correlated with both Dip-CFR (r=0.41; p=0.042) and CPT-CFR (r=0.579; p=0.002); moreover, DM patients in stage II/III of CKD (GFR