The role of the autonomic nervous system in postprandial hypotension was investigated. Sixteen elderly patients (age range from 67 to 92 years) and ten healthy controls (age range from 22 to 57 years) each ate a 600-kcal lunch. Arterial blood pressure was measured every 6 min prior to, during, and until 60 min after eating, and heart activity was recorded by 24-h Holter electrocardiogram. Heart rate variability was calculated every 5 min by the maximum entropy method. Very low frequency, low frequency and high frequency were expressed as a percentage of each mean value during daytime. Subjects were divided into three groups: with postprandial hypotension (n = 7); without postprandial hypotension (n = 9); and a control group. Low frequency during eating was greater in the group without postprandial hypotension (262.8 +/- 36.6%) than that in the control group (109.7 +/- 8.4%) and in the group with postprandial hypotension (170.3 +/- 20.8%) (p < 0.01). High frequency was the same among all three groups. Cumulative very low frequencies, calculated from the start of eating until 25 min after eating, were greater in the group without postprandial hypotension (6515 +/- 1128% x min) than in the control group (2940 +/- 412% x min) and in the group with postprandial hypotension (3441 +/- 520% x min) (p < 0.05). In order to prevent postprandial hypotension, a more than 200% increase in sympathetic nervous activity during eating is required compared with that of the mean daytime activity, thus making eating a significant cardiovascular load for the elderly.