Using a semiautomatic device (Remler), ambulatory blood pressure was recorded in ambulatory hypertensive patients who were either untreated (n = 55) or treated chronically with beta-blocking agents (n = 28), diuretics (n = 42), or a combination of both (n = 75). In all patients, one blood pressure reading was obtained during usual activities every 30 min for 12 h. The selection of untreated patients was based on clinic measurements (two to three repeated blood pressures of greater than 140/89 mm Hg). The mean systolic and diastolic blood pressures averaged from all patients over the whole day did not differ significantly among the groups, ranging from 133.7 to 141 mm Hg for the systolic and from 83.8 to 88.4 mm Hg for the diastolic. The variability of blood pressure, reflected by the difference between the average of the three highest and the three lowest values of the day, was not different among the four groups and ranged from 41.4 to 50.6 mm Hg for the systolic and from 30.1 to 34.4 mm Hg for the diastolic. Similarly, variability expressed as the standard deviation of the mean of all blood pressures measured during the day did not differ among the groups. In all groups, blood pressure was highest in the morning and lowest in early afternoon, and tended to rise again in the late afternoon. Thus, blood pressure variability of hypertensive patients is not changed by antihypertensive therapy with beta-blocking agents and/or diuretics.