SummaryVariability of blood pressure was studied in patients with normotension and hypertension. Supine blood pressures were recorded automatically with Arterio sonde (type 1217). Validity of the method was tested by recording blood pressure simultaneously with the mercury manometer and with Arteriosonde. Correlation coefficient for systolic and diastolic readings were 0.97 and 0.93 respectively. Blood pressure variability was calculated in three groups of 15 hospitalized patients: patients without cardiovascular diseases, patients in the third week of hospitalization for myocardial infarction and hypertensive patients. The higher the level of blood pressure, the higher was the variability of this pressure. However, when variability was expressed as the variation coefficient, the data in the three groups were no longer significantly different from each other. Finally it was shown that beta blockade with propranolol (160 and 320 mg/day) was unable to diminish variability of blood pressure recorded over a 24 hours period.