Objectives. Slow coronary flow (SCF) is slow progression of contrast agent in the coronary arteries in the absence of stenosis in epicardial coronary vessels. Endothelial dysfunction and diffuse atherosclerosis have been proposed for the etiology of SCF. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthesis, levels are associated with an increased risk of endothelial dysfunction and atherosclerosis. ADMA levels may be increased by homocysteine. The aim of this study was to evaluate the relationship between ADMA, nitric oxide and homocysteine in patients with SCF. Methods. The study group consisted of 50 patients with SCF. An age-and gender-matched control group was composed of 30 patients with normal coronary arteries and normal coronary flow on coronary angiography. We measured ADMA, nitric oxide and homocysteine plasma concentrations in all patients. Results. Plasma nitric oxide concentrations were significantly lower in the SCF group than in the control group (11.4 +/- 6, 16.1 +/- 9, p = 0.02). Plasma ADMA concentrations (0.9 +/- 0.3, 0.7 +/- 0.3, p = 0.01) and plasma homocysteine concentrations (12.4 +/- 5, 9.8 +/- 2, p = 0.03) were significantly higher in the SCF group than control group. The mean TIMI frame count (TFC) was significantly correlated with plasma ADMA (r = 0.26, p = 0.02) and homocysteine (r = 0.28, p = 0.02) concentrations, but not with nitric oxide concentrations (r = -0.18, p = 0.13). In linear regression analysis, plasma ADMA concentrations (beta = 4.6, p = 0.005) and homocysteine concentrations (beta = 0.2, p = 0.03) were independently and positively associated with mean TFC. Conclusion. Our results suggest that plasma concentrations of ADMA and homocysteine are increased in SCF and also that these are independent predictors of SCF.