Objectives: In vitro studies suggest an influence of hyperhomocysteinemia on the coagulation system, but the influence of mild hyperhomocysteinemia in vivo is unclear.
Methods And Results: We studied the relation between homocysteine and markers of coagulation activation and endothelial cell activation in 279 patients with established atherosclerotic disease. In addition, we performed an investigator-blinded placebo-controlled cross-over study to investigate the influence of acute hyperhomocysteinemia by oral methionine load on these markers in 20 healthy volunteers.