Twenty-four-hour blood pressure (BP) was determined noninvasively in 11 ambulatory (active group, 78 +/- 2 years old) and 11 bedridden (passive group, 79 +/- 2 years old) elderly patients. Postprandial reduction in BP was evident in both groups. BP variability during the daytime was significantly greater in the active group than in the passive group. Consequently, only patients of the passive group showed a significant day-night difference in BP and a significant circadian rhythm of BP as well. We conclude the following: 1) postprandial reduction in BP contributes to BP variability during daytime in elderly patients, 2) the greater BP variability seen in ambulatory patients obscures the day-night rhythm of BP, and 3) the day-night rhythm of BP exists in bedridden patients.