Most exercise radionuclide studies utilise the supine bicycle ergometer during imaging, although exercise on a treadmill results in greater cardiovascular stress. Twenty-three patients were studied to compare the radionuclide left ventricular ejection fraction (LVEF) estimated immediately following treadmill exercise with that obtained at peak supine bicycle exercise in patients with coronary artery disease (CAD) and patients with normal coronary arteries. In 14 patients with CAD the rest LVEF was 47 +/- 7% (mean +/- SD) by first pass and 49 +/- 10% by equilibrium blood pool techniques. Immediately following maximum treadmill exercise, 13 of the 14 patients with coronary artery disease showed either no change or a decrease in LVEF, the LVEF was 49 +/- 7% (P = NS) and 47 +/- 8% (P = NS) by first pass and equilibrium determinations respectively. In comparison the LVEF during peak supine bicycle exercise decreased significantly to 42 +/- 12% (P less than 0.01). In nine patients with angiographically normal coronary arteries the rest LVEF was 51 +/- 4% by first pass and 54 +/- 6% by equilibrium, increasing to 67 +/- 7% (P less than 0.01) and 64 +/- 7% (P less than 0.01) respectively following treadmill exercise. During peak bicycle exercise LVEF increased in the normal patients to 61 +/- 7% (P less than 0.05). These data suggest that quantitative radionuclide angiography following either maximum treadmill exercise or during peak bicycle exercise can discriminate between patients with coronary artery disease and normal subjects, although the magnitude of left ventricular functional changes are greater during bicycle stress.