One hundred and seventy-three Arab patients with non-insulin-dependent diabetes mellitus (NIDDM) and 51 controls were examined. The routine laboratory tests of fasting blood sugar (FBS), glycosylated hemoglobin (HbA1c), fructosamine (FRA), and triglycerides (TG) were compared with lipid hydroperoxides (LHP) as detected by the thiobarbituric acid (TBA) method, which measures total TBA reacting substances (TBARS). All routine laboratory measures were elevated in the patient population. In the case of LHP, values in NIDDM were 491 +/- 183 mumol/L for men and 507 +/- 183 mumol/L for women, as compared with pooled normal values of 275 +/- 85 mumol/L. Seven patients with NIDDM undergoing hemodialysis were also elevated above normal (441 +/- 97 mumol/L). Comparisons between LHP and the other biochemical parameters indicated a positive statistical correlation with triglycerides (p less than 0.001); FBS, HbA1c, and FRA (p greater than 0.01). Patients with NIDDM on dietary control had somewhat lower LHP levels (441 +/- 135 mumol/L) than those receiving insulin (519 +/- 206 mumol/L), or oral hypoglycemic agents (518 +/- 177 mumol/L). Dietary maintenance also resulted in reduced FBS and HbA1c levels. Subdivision of patients according to duration of disease and by nationality showed that Kuwaiti nationals had slightly higher LHP values than did patients of other Arabic origin. Women patients (Kuwaiti and non-Kuwaiti) with NIDDM disease duration of greater than 10 years, had LHP levels above those of males (551 +/- 245 versus 478 +/- 126 mumol/L) and, as a group, showed significant enhancement of retinal complications (85.5% versus 55%). A statistically significant trend (p less than 0.08) could be demonstrated between the prevalence of retinopathy and increasing serum LHP levels.(ABSTRACT TRUNCATED AT 250 WORDS)