Over the past 10 years, extensive studies have been conducted in Turkey to determine the risk factors for heart disease. Studies involving approximately 10,000 Turkish men and women from six different regions of Turkey have established that this population is unique in several ways. The Turks have the lowest plasma levels of high density lipoprotein cholesterol (HDL-C) of almost any population in the world (75 percent of the men and 50 percent of the women have HDL-C levels <40 mg/dl). The mean HDL-C levels are 10-15 mg/dl lower than those in Western European or American populations. In addition, Turks, especially Turkish women, have a tendency toward obesity [38.8 percent of the women have body mass index (BMI) >30 kg/M2], and both men and women have a tendency toward hypertriglyceridemia. The low HDL-C, however, is independent of obesity or hypertriglyceridemia. Samples from this well-characterized population provide a unique opportunity to explore the genetic determinants associated with the high prevalence of low HDL-C, hypertriglyceridemia, and obesity (characteristics of the metabolic syndrome).