Seventy two consecutive patients without a history of diabetes and normal fasting plasma glucose were included in this study of insulin levels. Standard oral glucose tolerance test with 75 gm glucose and fasting and two hour insulin levels were estimated in all patients. Coronary artery disease (CAD) was confirmed or excluded by selective coronary arteriography. In 20 patients, CAD was diagnosed by electrocardiographic (ECG) and clinical evidence of earlier myocardial infarction. Mean fasting plasma insulin was 31.40 +/- 22.2 IU/dl in the CAD positive and 32.3 +/- 13.6 IU/dl in the CAD negative group. The mean two hour plasma insulin was 274.6 +/- 301.1 IU/dl in the CAD positive and 104.8 +/- 74.9 IU/dl in the CAD negative group (p < 0.04). Two hour plasma insulin levels were significantly higher in patients with atherosclerotic coronary artery disease. It is concluded that the estimation of a two hour plasma insulin level after 75 gm of glucose load, could help differentiate CAD from normals.