The onset of sepsis is often non-specific, and its severity is cryptic. The pathophysiological mechanism of sepsis development involves vascular alteration and, in particular, the impairment of endothelial function. Aim of the study was to evaluate the potential implications of brachial endothelial function assessment in patients affected by Gram-negative sepsis. Forty-five young patients (mean age 41+/-8 years, 18 males) with Gram-negative sepsis were included; at admission time (T0) signs and symptoms, clinical and laboratory data were collected; the Sequential Organ Failure Assessment (SOFA) score was assessed at the time of the access along with the evaluation of brachial flow-mediated vasodilation (FMV). The same parameters were repeated 3 days after hospitalization (T1). Study population at the hospitalization time was divided on the basis of a brachial FMV cut off: at the T0 subjects with FMV<7.5% had lower white blood cell count in comparison to subjects with FMV> or =7.5% (6693+/-1559 mmc versus 14,270+/-2399 mmc); subjects with FMV<7.5% had a significant increase in SOFA score at T1 (4+/-1 versus 6+/-1) and a significant reduction of brachial FMV at T1 (4.8+/-2.7% versus 3.7+/-2.6%) (all p<0.05). FMV at the admission time was predicted by white blood cells (beta=0.65; p<0.001) and brachial diameter (beta=-0.292; p<0.05); Delta changes in FMV were predicted by changes in SOFA score (beta=-0.41; p<0.05). In conclusion, the present study indicates that in the initial phase of sepsis an impairment of brachial FMV anticipated the progression in organ failures; these considerations support the potential utility of brachial FMV in clinical practice in acute pathologies as septic state.