In this study, self-determined, ambulatory and casual blood pressure measurements were studied in patients with mild to moderate essential hypertension. 31 patients were studied during a 7-day period: casual blood pressures were taken on the 1st, 4th and 7th day. Pressure monitoring for 24 h using a noninvasive ambulatory blood pressure recorder was performed on the 1st and 7th day. Patients recorded blood pressure daily at home at least 3 times each day. On the 1st day, the mean casual blood pressure was significantly higher than either mean self-determined blood pressure or mean 24-hour ambulatory blood pressure. There was no significant difference between ambulatory daytime means and self-determined means. Casual blood pressures decreased from day 1 to day 7 significantly, while no significant difference in self-determined or ambulatory readings was observed. On the 7th day casual blood pressures were still significantly higher than self-determined measurements. Our results show that values obtained from daytime ambulatory measurements and self-determined measurements were equivalent. A fall in blood pressure with serial observations was found only in casual blood pressure, while no significant change occurred with either self-determined or ambulatory pressure. Since self-determined blood pressure measurements are easier and more economical to perform than ambulatory measurements, self-determined measurement is an excellent alternative to obtain representative blood pressure values for the diagnosis and treatment of hypertension.