Ambulatory recordings of blood pressure (BP) and heart rate were performed using a Spacelabs device during day and night periods in parkinsonian patients with (n = 19) or without (n = 19) orthostatic hypotension. In patients with orthostatic hypotension, the average blood pressure during the night (systolic BP: 137 +/- 5 mmHg; diastolic BP: 80 +/- 3 mmHg) was higher (p < 0.05) than during the diurnal period (systolic BP: 121 +/- 3 mmHg; diastolic BP: 76 +/- 2 mmHg). In parkinsonian patients without orthostatic hypotension, a physiological decrease in BP was recorded during the nocturnal period. In patients with orthostatic hypotension, BP variability was higher (p < 0.05) during the day (systolic BP: 14.6 +/- 1.3%, diastolic BP: 16.5 +/- 1.0%) than during the night (systolic BP: 9.1 +/- 0.8%, diastolic BP: 10.8 +/- 1.1%). The blood pressure load (% of BP values above 140/90 mmHg) during the night was significantly higher (p < 0.05) than during the day for both systolic (41.2 +/- 8.1 vs 19.6 +/- 4.7%) and diastolic BP (24.9 +/- 6.9 vs 16.3 +/- 4.9%). A normal decrease in heart rate was found in both groups during the night. A fall of at least 25 mmHg in systolic BP after meals occurred in 10 patients with orthostatic hypotension and in 1 without orthostatic hypotension. These results indicate that orthostatic hypotension in Parkinson's disease is associated with specific modifications of ambulatory blood pressure including loss of circadian rhythm of BP, increased diurnal BP variability and often post-prandial hypotension.