The goal of this work is to study the consequences of the last on variations of the blood pressure (BP) in the course of 24 hours. From 1994 to 1997 we have selected 99 hypertensive patients and studied their BP profile. This study included 72 women and 27 men. Their age varies from 22 to 72 years (average 56.7 +/- 9 years). All these patients has an ambulatory blood pressure measurement (ABPM) before the fast and during Ramadan. Before Ramadan the period of the sleep goes from 10 pm +/- 1 h to 8 am +/- 1 h. During the month of Ramadan, the sleep lasts from 0 h +/- 1 to 9 am +/- 1 h. [table: see text] No statistically significant difference is noted between these 2 periods neither for the systolic BP (SBP) nor for the diastolic BP (DBP), for the BP of 24 hours, and the diurnal and nocturnal periods. We have then the compared the hourly average on 24 hours of the 99 patients. We observed that during the month of Ramadan the peak of the awakening is delayed by 2 hours and the nocturnal through is delayed by 1 hour. After this study, which is the first one to deal with variations of blood pressure during the fast of Ramadan we can confirm that in patients with essential hypertension without complications, the fast is well supported. The variations of BP are minimal and are related to the variations of the sleep, activity and eating pattern.