The relation between the increase in oxygen uptake (VO2) and increase in work rate (WR) between unloaded pedaling and maximal work during incremental cycle ergometer exercise was studied in normal men, men with uncomplicated systemic hypertension and ambulatory men with various cardiovascular diseases. The postulation was that impaired peripheral oxygen delivery would reduce the ratio of the oxygen utilized relative to work performed. The ratio of increase in VO2 to increase in WR (delta VO2/delta WR) was relatively constant: 10.29 +/- 1.01 ml/min/W in normal men (n = 54) for exercise 6 to 14 minutes in duration with uniform work increments of 15, 20, 25 or 30 W/min, regardless of age. The value in men with uncomplicated systemic hypertension (n = 24) was not significantly different from that of normal men. However, more than half of the men with peripheral vascular disease (n = 7) or pulmonary vascular disease (n = 5) or men who had electrocardiographic abnormalities during exercise (n = 39) had a significantly lower delta VO2/delta WR, 8.29 +/- 1.17 ml/min/W (p less than 0.05) especially evident as maximal work rates were approached. Thus, delta VO2/delta WR during incremental exercise testing is predictable for normal men and a reduction in this ratio indicates cardiovascular dysfunction.