Exercise-induced ST-segment depression is a marker of impaired prognosis in patients with suspected or manifest CAD. Whether ST-segment depression remains of prognostic importance, after exercise tolerance and extent of CAD have been considered, is unknown. We analysed the prognostic importance of exercise-induced ST-segment depression (greater than 0.15 mV) in 1250 medically treated patients with angiographically determined CAD (mean follow-up after angiography 4.5 years). Based on exercise tolerance (supine bicycle ergometry) patients were divided into two groups: group A patients (n = 677) with lower exercise tolerance (less than or equal to 75 W) and group B patients (n = 573) with better exercise tolerance (greater than 75 W). Group A patients had a lower 5-year survival rate than group B patients (81.5% versus 94%, P less than 0.00001). In group A, patients with ST-segment depression had a lower 5-year survival rate than patients without ST-segment depression (76% versus 85%, P = 0.01). In group B, patients with and without ST-segment depression had similar 5-year survival rates (90% versus 96%, P = 0.11). Subgroup analysis of groups A and B according to number of diseased vessels and presence or absence of ST-segment depression revealed that exercise-induced ST-segment depression (greater than 0.15 mV) was of additional prognostic importance only in patients with triple vessel disease. 5-year survival rates in group A with triple vessel disease were 71% with and 80% (P = 0.057) without ST-segment depression.(ABSTRACT TRUNCATED AT 250 WORDS)