The metabolic syndrome (MS) as defined by the National Cholesterol Education Programme Adult Treatment Panel III (ATP-III) predisposes to the formation of atherosclerosis [1]. Multiple previous studies have demonstrated that vascular endothelial dysfunction (ED) and systemic inflammation can act as independent predictors of future cardiovascular (CVS) complications [2,3]. We have investigated the relationship between ED/inflammation in healthy subjects with/without the ATP-III criteria for the MS. Sixty four (26 male; mean age (years) with MS 40.7±10.9, without MS 34.7±6.3) healthy non-diabetic non-smokers were screened for MS and divided into two groups depending on the presence/absence of MS. Inflammatory markers (C-reactive protein (CRP), tumour necrosis factor-alpha receptor-2 (TNF, a marker of TNF-alpha activity), interleukin-6 (IL-6)) brachial artery flow mediated dilation (FMD, a measure of endothelial function), insulin resistance (using the homeostasis assessment (HOMA)) [4] were compared in both groups. CRP was measured using high-sensitivity turbidimetric immunoassay and TNF/IL-6 using enzyme-linked immunosorbent assay. High resolution ultrasound was used to assess FMD. Brachial artery diameter was measured at baseline, blood flow occluded with a pneumatic cuff in the forearm for 5 min and artery diameter re-measured approximately 40 s after deflation of the cuff. FMD was expressed as the percentage change in brachial artery diameter from baseline. Values are presented as mean ± S.D. Student’s t test was used to analyse differences between subjects with/without MS. Analysis of variance with linear trend was used to assess correlation between variables and ATP-III diagnostic criteria. Statistical significance was accepted at p<0.05. FMD values were significantly lower and TNF, IL6 and HOMA higher in subjects with MS. There was no difference in CRP levels. One-way analysis of variance showed a significant linear trend between FMD (p<0.001, R²=0.25) and a positive trend between logHOMA (p<0.001, R²=0.40), logIL6 (p<0.001, R²=0.23) and log TNF (p=0.01, R²=0.10) and the number of diagnostic characteristics of the ATP-III criteria present in each subject. Healthy subjects with the MS have greater ED and systemic inflammation in comparison to healthy subjects without the MS. These changes have independently been shown to be associated with an elevated risk of future CVS complications. Furthermore, the extent of endothelial dysfunction, insulin resistance and inflammation increases with the presence of each additional ATP-III diagnostic criteria. We did not identify a significant difference in CRP levels between the two groups.