Various samples of cfDNA added to endothelial cell cultures resulted in a number of effects. cfDNA in concentrations similar to those in human blood plasma caused an increase in NO synthesis in endothelial cells. In addition, cfDNA isolated from blood from patients with cardiovascular diseases influenced ROS synthesis more efficiently than cfDNA from healthy donors. Also, the ability of cfDNA to influence the elaboration of NO and ROS depends on the sample concentration and the content of CG-DNA marker.