Aim: To investigate the effect of hemodialysis on blood pressure by monitoring ambulatory blood pressure during the interdialysis period and to evaluate the relationship between hypertension and the percentage of total body water calculated via bioelectrical impedance analysis. Methods: Twenty five patients with end stage renal disease who were in the hemodialysis program were included in the study. But only fifteen patients had been able to stay in the required criteria till the end. Pre- and post-dialysis blood pressures of the patients were measured manually and ambulatory blood pressure measurements were obtained during the interdialysis period. Measurements of total body water were performed with bioelectrical impedance method following the hemodialysis procedure. The patients were evaluated for daily course of blood pressure, use of anti-hypertensive medications, incidence of the falling rate of blood pressure at night, amount of total body water and interdialysis weight gain. Results: Manual pre- and post-dialysis measurements and mean values of 44 hours' ambulatory blood pressure monitoring were found to be similar. Blood pressures were found to be significantly low until the 24th hour and they were increased at the 2nd day, then returned to initial levels at the 44th hour. There was uncontrolled hypertension in 7 of the 11 hypertensive patients (63.6 %). Mean percentage of total body water was higher in patients with hypertension (61.1 ±9.8 vs. 57.9±7.0, p>0.05). Conclusion: In our study, the reducing effect of hemodialysis on blood pressure was observed and this effect has continued nearly 24 hours after the dialysis. The fact that total body water is more in hypertensive patients supports the idea that volume excess is an important factor responsible from hypertension.