We examined the plasma lipids, lipoproteins, and selected apolipoproteins in approximately 9,000 men and women from six different regions of Turkey with markedly different diets, ranging from an Aegean coast diet high in olive oil (plasma cholesteryl ester fatty acids enriched in monounsaturated fatty acids) to an inland Anatolian diet high in meat and dairy products (plasma cholesteryl esters enriched in saturated fatty acids). The rural population consuming an olive oil-rich diet had the lowest plasma cholesterol levels (men, 149 mg/dl; women, 150 mg/dl). The urban populations of Istanbul and Adana had higher plasma cholesterol levels (men, 202 and 184 mg/dl, respectively; women, 181 and 190 mg/dl, respectively). Affluent men had the highest cholesterol levels (207 mg/dl). The low density lipoprotein (LDL) cholesterol levels tended to parallel the total cholesterol levels (highest for Istanbul men at 136 mg/dl and lowest for Aegean coast men and women at approximately 100 mg/dl). Strikingly, the Turkish people were found to have very low levels of high density lipoprotein (HDL) cholesterol (HDL-C) (mean values for all six regions: men, 34-38 mg/dl; women, 37-45 mg/dl) and total cholesterol/HDL-C ratios that were high (mean values for all six regions: men, 4.5-5.5; women, 3.9-5.0). The low HDL-C levels appear to be caused, at least in part, by a genetic factor. Triglyceride levels also tended to be high in Turkish men (approximately 120-150 mg/dl) and women (approximately 90-110 mg/dl). Thus, even though the total plasma cholesterol levels are not excessively elevated in comparison to those in other populations, the presence of low HDL-C or low HDL-C coupled with mildly elevated triglyceride levels may represent a significant risk factor for heart disease in the Turkish population. Affluence and higher education were associated with higher cholesterol levels. Lack of physical activity, smoking, and alcohol consumption also tended to be associated with a detrimental lipid profile. Lipoprotein[a] levels were identical among the regions surveyed (mean: 11-15 mg/dl) and displayed the typical distribution with an increased number of individuals with low levels. The 90th percentile value for lipoprotein[a] was about 30 mg/dl for both men and women. Smoking, a major risk factor for heart disease, was very prevalent in the Turkish population, especially in men (50-70% smokers) and women in urban areas (30-40% smokers). Hypertension, defined as a systolic pressure > 140 or a diastolic pressure of > 90 occurred in approximately 17% and 26% of the men and women surveyed, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)