A circadian distribution of ischaemic events has been identified in ambulatory patients with stable angina. However, whether a similar distribution occurs in patients with unstable angina who remain at bed rest is still uncertain. Therefore, we analysed the possible circadian presentation of episodes of angina at rest (n = 1222) in 193 patients hospitalized consecutively. The influence of extent of coronary disease (number of vessels with > 70% stenosis, 0, 1 and 2-3), type of ECG changes during pain on a 12-lead ECG, and coronary reserve, as assessed by ischaemic threshold (atrial pacing), were also evaluated. There were two peaks of highest incidence: at 0700-1000h and at 1900-2200h (P < 0.0001) which were unrelated to the extent of coronary disease, coronary reserve or type of ECG change. Patients with 1 or 2-3 vessel disease with a reduced ischaemic threshold (= < 150 beats.min-1), however, had a higher incidence of midnight angina (2300-0200h) than those with a normal threshold or with no vessel disease (P < 0.001). It is concluded that, in spite of being at bed rest, patients with unstable angina present a definite circadian distribution of angina, with peaks in the early morning and late evening. Patients with a low coronary reserve seem to have a higher incidence of midnight angina than others.