BACKGROUND In cardiac transplant recipients, long-term survival may be limited by transplant coronary artery disease (TxCAD). Hyperhomocysteinemia (Hhcy) has been associated with vascular disease and is common in transplant recipients. The objective of this study was to determine the relationship between fasting homocysteine (Hcy) concentrations and TxCAD in a cohort of cardiac transplant recipients. METHODS Forty-eight patients more than 5 yr after transplant were recruited from a cohort of 72 consecutive patients with in-depth analysis of homocysteine levels from the Cardiac Transplant Clinic. Early morning fasting blood was obtained, and the plasma separated and frozen within 30 min. Hcy concentrations were determined by high-performance liquid chromatography (HPLC) with pulsed integrated amperometry. Coronary angiograms were reviewed in a blinded fashion. TxCAD was diagnosed, using the most recent angiogram, when a >25% lesion was present anywhere in the coronary tree. RESULTS Forty-eight patients transplanted between 1985 and 1994 were studied. The mean Hcy concentration for the cohort was 23.5+/-5.0 micromol/L, all patients had homocysteine levels above the upper range of normal (5-15 micromol/L). Hcy concentrations were significantly higher in patients with angiographic evidence of TxCAD: 25.0+/-5.9 vs. 21.9+/-3.4 micromol/L, p=0.03. This effect persisted when covariates were taken into account using logistic regression analysis. CONCLUSIONS Hhcy is associated with TxCAD. Prospective studies are required to confirm this association and to assess the efficacy of Hcy-lowering therapy in this patient population.