We compared the characteristics of silent and painful ischaemia during ambulatory ST segment monitoring in 288 patients with documented coronary arterial disease and stable angina. During 12,436 hours of monitoring, 890 ischaemic episodes were recorded, of which 652 (73%) were silent. Silent and painful ischaemic episodes were similar in terms of heart rate at onset of ischaemia, increase in heart rate prior to ischaemia, duration of ischaemia, and percentage of episodes not preceded by an increase in heart rate. Change in the mean maximal ST segment was greater during painful ischaemic episodes (P less than 0.01). Silent ischaemia is characteristically painful ischaemia without the pain.