Syndrome X consists of low serum high density lipoprotein-cholesterol (HDL-C), raised serum triglyceride, glucose intolerance, increased blood pressure, abdominal obesity and insulin resistance which is associated with increased risk of coronary heart disease (CHD). Apolipoprotein (apo) A-I containing lipoprotein particles, lipoprotein A-I (Lp A-I) and lipoprotein A-I:A-II (Lp A-I:A-II.) may have different metabolic functions. The purpose of this study was to evaluate the relationship between insulin and apo A-I containing lipoproteins in syndrome X patients with or without CHD. We selected 38 male patients with syndrome X and divided into two groups: The one with CHD (n=21) and the other without CHD (n=17). Third group including 22 normal male subjects was the control group. We measured fasting blood glucose, cholesterol, triglyceride, low density lipoprotein-cholesterol (LDL-C), HDL-C, apo A-I, apo B, Lp A-I, Lp A-I:A-II and insulin, and 2-h glucose and insulin levels after a 75 g oral glucose tolerance test in all subjects. In both syndrome X groups, serum levels of triglyceride, apo B, fasting glucose and insulin, and 2-h glucose and insulin were significantly increased (p