Since there is experimental evidence that insulin promotes atherosclerosis, we tested the hypothesis that insulin levels are higher in patients with diffuse atherosclerotic coronary artery disease by measuring insulin levels in 46 nondiabetic patients with angiographically defined diffuse coronary artery disease and 46 normal controls with angiographically normal coronary arteries. Fasting insulin levels were similar in both groups of patients: 7.70 +/- 5.77 microU/mL in those with diffuse coronary disease versus 7.39 +/- 5.01 microU/mL in controls. Also, insulin levels drawn 1 and 2 h after oral glucose challenge were not significantly different in patients with diffuse disease (48.78 +/- 32.46 microU/mL and 42.26 +/- 32.38 microU/mL, respectively) compared with patients with normal coronary arteries (51.03 +/- 28.01 microU/mL and 43.79 +/- 31.62 microU/mL, respectively). We conclude that insulin probably does not promote clinical atherosclerosis in nondiabetics.