Objective - Many studies have demonstrated a strong association between elevated plasma total homocysteine (Hcy) levels and vascular disease. The objective of this study was to examine the relation between homocysteine levels and coronary artery disease in Turkish patients. Methods and results - In this study plasma homocysteine levels were measured in control and patient groups. A significant coronary artery lesion was defined as a stenosis of ≥70% as shown by coronary angiography and determined by on-line quantitative measurements; treatment was by coronary angioplasty. Total plasma Hcy level was measured before the coronary intervention. Plasma homocysteine levels were measured by an HPLC method in patients with a definite diagnosis of coronary artery disease and compared with age- and sex-matched controls. Patients with coronary artery disease had significantly higher mean homocysteine concentrations than control subjects (geometric mean ± 95% Cl: 12.5 ± 1.1 μmol/l vs. 8.60± 1.07 μmol/l, p<0.00 1). Eighty-three (59%) members of the patient group and 14 (21%) members of the control group had plasma homocysteine concentrations above the 11.3 μmol/l, which represents the concentration which includes the uppermost quintile of the control group distribution (odds ratio 4.35, 95% Cl; 2.1-8.94). Conclusion - Results of this study indicate that high plasma levels of homocysteine in Turkish subjects are associated with coronary artery disease. Our data suggest that focusing public health initiatives on this issue may reduce the high prevalence of cardiovascular disease in the Turkish population.