OBJECTIVE This paper aims to determine whether disease activity, systemic inflammation and metabolic syndrome are potential determinants of circulating asymmetric dimethylarginine (ADMA) in ankylosing spondylitis (AS) patients undergoing TNF-α antagonist-infliximab-therapy. METHODS We investigated ADMA serum concentrations in a series of 30 non-diabetic AS patients without history of cardiovascular (CV) events that were treated with the TNF-α antagonist infliximab, immediately prior to an infliximab infusion. Correlations of ADMA serum levels with disease activity, systemic inflammation and metabolic syndrome were assessed. Also, potential changes in ADMA concentration following an infusion of the anti-TNF-α monoclonal antibody-infliximab were analysed. RESULTS A higher concentrations of ADMA in men (p=0.012) and patients with hypertension was found (p=0.001). There was also a marginally positive correlation of ADMA serum levels with C-reactive protein levels (p=0.08). Moreover, a significant negative correlation between ADMA levels and total cholesterol and LDL-cholesterol was observed (p= 0.05). No differences in ADMA levels according to the specific clinical features of the disease were seen. A single infliximab infusion did not lead to significant changes in ADMA serum levels. CONCLUSIONS In AS patients undergoing periodical treatment with the anti-TNF-α monoclonal antibody-infliximab a link between some features of metabolic syndrome and ADMA concentrations was observed.