1. Ambulatory blood pressure monitoring was carried out in 10 subjects for a period of 48 h, the first or second 24 h part of which was selected randomly to be a period of complete bed rest.
2. Heart rate was significantly lower throughout the period of bed rest except for the period 04.00–08.00 hours, when there was little difference.
3. The circadian variation of blood pressure was reduced during the day of bed rest but this was mainly due to higher night-time pressures.