Endothelial function is impaired in first-degree relatives (FDRs) of patients with type 2 diabetes. Many states characterized by endothelial dysfunction are associated with increased cardiovascular sympathetic outflow. In this study, we investigated endothelial and autonomic nervous system (ANS) functioning in FDRs and tested the hypothesis that in basal condition, impaired endothelial function is associated with impaired cardiovascular ANS regulation. Flow-mediated endothelium-dependent and -independent vasodilation of the brachial artery was measured with high-resolution ultrasound in 27 otherwise healthy FDRs (14 men and 13 women; mean age 32 years) with normal oral glucose tolerance and in 15 age- and gender-matched control subjects. Cardiovascular ANS regulation was investigated by means of spectral analysis of heart rate and systolic blood pressure (SBP) variability. Baroreflex sensitivity was assessed by the spontaneous baroreflex sequences technique. Flow-mediated endothelium-dependent vasodilation was 9.4+/-1.0% in FDRs and 17.0+/-2.3% in control subjects (P=0.001). Low-frequency oscillations in SBP variability were 8.6+/-2.8 and 2.8+/-0.6 mm Hg in FDRs and controls, respectively (P=0.04). Baroreflex sensitivity was significantly less in FDRs than controls (22.8+/-2.7 versus 37.0+/-5.8, respectively; P=0.01). Change in vessel diameter was inversely correlated with the low-frequency component of SBP variability (r=-0.40; P=0.014). In healthy FDRs of diabetic patients there is a concomitant, possibly related, impairment in endothelial and ANS functioning, which manifests, indirectly, with increase in vascular sympathetic outflow and a depressed baroreflex, vagal, control of heart rate.