Hemodynamic profiles at rest and during bicycle exercise are described in 50 normal male subjects. In nine of these, the hemodynamics at rest and during exercise in the supine position have been compared to those in the sitting position. In the supine position, the observed and derived hemodynamic parameters at rest and during exercise (mean +/- standard deviation) were: heart rate 77 +/- 11 vs 127 +/- 17 beats . min-1, brachial arterial mean pressure, 12.4 +/- 1.2 vs 15.0 +/- 1.6 kPa (93 +/- 9 vs 113 +/- 12 mmHg), pulmonary arterial mean pressure 1.9 +/- 0.5 vs 3.2 +/- 0.8 kPa (14 +/- 4 vs 24 +/- 6 mmHg), left ventricular end-diastolic pressure 1.2 +/- 0.4 vs 1.7 +/- 0.7 kPa (9 +/- 3 vs 13 +/- 5 mmHg), cardiac output 6.3 +/- 1.5 vs 12.0 +/- 3.0 1 . min-1, stroke volume 88 +/- 22 vs 95 +/- 23 cm3, and left ventricular stroke work 0.93 +/- 0.27 vs 1.26 +/- 0.34 J . beats-1. Comparison of hemodynamic data in the supine and sitting position showed that pulmonary capillary wedge pressure, left ventricular end-diastolic pressure, cardiac output, stroke volume, and left ventricular stroke work were lower and heart rate higher in the sitting position, while brachial arterial and pulmonary arterial mean pressures were similar in the two positions. During exercise, the absolute values of pulmonary capillary wedge pressure, left ventricular end-diastolic pressure and stroke volume were lower and heart rate higher in the sitting position, while cardiac output and left ventricular stroke work were similar in the two positions. Comparison of changes from rest to exercise in the supine and sitting postures revealed similar increases in heart rate, pulmonary capillary wedge pressure, left ventricular end-diastolic pressure, cardiac output, and stroke volume in the two positions.