Circulating endothelial cells (CECs) are a marker of endothelial injury and endothelial dysfunction. We measured CECs in 95 patients with functioning renal transplants at risk of premature cardiovascular (CV) disease and in normal control subjects. We were unable to demonstrate consistent relationships between CEC levels and conventional CV risk factors in transplant recipients. However, CEC levels were increased in patients with a history of rejection. We conclude that CECs are of little use as a marker of CV risk in this population but may be a useful marker to monitor allograft rejection.