The specific features of circadian rhythm of BP were investigated in freely moving male SHR rats using telemetry monitoring technique. BP was recorded in the abdominal aorta according to 24-h/4-month schedule. The data were obtained from 22, 26, 30, 34, and 38-week-old animals. Normotensive Wistar rats (22 weeks) served as the control. It was found that the mean 24-h, daytime, and nighttime systolic and diastolic BP in hypertensive rats significantly surpassed the control throughout the observation period and practically did not change during prolonged hypertension. Some prognostically negative changes in the circadian rhythm of the basic hemodynamics system parameters appeared with time. For instance, the maximum 24-h systolic BP significantly increased in comparison with the initial level.