Six untreated hypertensive patients and ten on therapy, but having elevated blood pressures, were treated with coenzyme Q10(CoQ10); 14/16 patients showed reductions (p less than 0.05-less than 0.001) in systolic pressures; 11/16 showed reductions (p less than 0.05-less than 0.001) in diastolic pressure; 9/10 showed reductions of elevated pressures to a normal range. By impedance cardiography and electrocardiography, there were no changes in cardiac outputs, stroke volumes and Heather Indices except for a few patients with changes of doubtful biological significance. 3/16 patients had exceptionally low basal specific activities of the succinate dehydrogenase-coenzyme Q10 reductase in blood which increased to a normal range on treatment. A greater deficiency of CoQ10 in the vascular system than in blood is likely. We consider that (1) the mechanism of reduction of elevated blood pressures by CoQ10 is based upon normalization or autoregulation of peripheral resistance rather than cardiac regulation, and (2) that the therapeutic activity of CoQ10 is not pharmacodynamic, but results from a translational increase in levels of CoQ10-enzymes in vascular tissue during ca. 4-12 weeks.