The effects of insulin on the lipid values of nonobese non-insulin-dependent diabetic (NIDDM) Arab women requiring insulin was investigated to find whether these patients have the same coronary artery risk factor related to lipid levels. In this study, 55 NIDDM women on insulin therapy (mean age 28 +/- 8.1 yr and duration of disease 5 +/- 1.2 yr) and 70 control subjects (matched for sex, age, and body mass index) were studied for their plasma levels of lipids, lipoproteins, and apolipoproteins. Concentrations of total cholesterol, very-low-density lipoprotein cholesterol, low-density lipoprotein (LDL) cholesterol, triglyceride (TG), LDL TG, high-density lipoprotein triglyceride (HDL TG), phospholipid, glucose, glycosylated hemoglobin (HbAtc), apolipoprotein B (apoB), LDL-apoB, and apoB/apoAl were significantly elevated in diabetic women compared with control subjects. There was no significant change in the levels of apoAll in plasma and lipoprotein fractions. Concentrations of HDL cholesterol (chol), HDL2-chol, HDL3-chol, plasma apoAl, HDL2-apoAl, HDL3-apoAl, and HDL-apoAl were significantly lower in diabetic women than in control subjects. There was no significant correlation between glucose or HbAtc and most of the lipids, lipoprotein lipids, and apolipoproteins measured. Despite normal body weight and insulin therapy, abnormalities in lipids, lipoprotein lipids, and apoB persisted in NIDDM patients compared with control subjects. Our data may favor an enhanced affinity toward atherosclerosis in these patients.