Autorhythmometry of blood pressure by an individual over an age-span of 67 to 72 years showed a strong circadian rhythm superimposed upon significant circaseptan and circannual rhythms. Automatic BP monitoring with an Arteriosonde throughout 24-hour spans on 4 separate occasions, before and during treatment, also indicated a prominent circadian BP rhythm and a treatment-related reduction in circadian mesor. The concept of a blood pressure mesor reference for the antimesor-hypertensive treatment constitutes a valuable guideline in the control of "familial" mesor-hypertension.