The increase of circulating asymmetric dimethylarginine (ADMA) concentrations, a competitive inhibitor of the nitric oxide synthases, is associated with an increased cardiovascular risk and is considered to play a role in endothelial dysfunction. Recently, ADMA production was observed in stimulated human peripheral mononuclear cells. In this study, we examined a potential relationship between concentrations of ADMA and of the immune activation marker neopterin in patients scheduled for coronary angiography. In a cross-sectional approach, blood concentrations of ADMA, homocysteine, neopterin, folic acid and vitamins B6 and B12 were compared in 2030 patients, which were recruited as participants of the LUdwigshafen RIsk and Cardiovascular Health (LURIC) study. ADMA concentrations did not differ between patients with coronary artery disease (CAD) (mean +/- SD: 0.82 +/- 0.15 micromol/l) and controls (0.81 +/- 0.14 micromol/l; Welch's t-test: P = n.s.). ADMA concentrations correlated with homocysteine (r(s) = 0.207) and vitamin B6 (r(s) = -0.190), and an even stronger correlation with neopterin (r(s) = 0.276; all P < 0.0001) was observed. In conclusion, increased ADMA concentrations in patients at risk for atherosclerosis are associated with increased neopterin concentrations. Data suggest that immune activation may contribute to increased ADMA production in CAD patients.