This study was designed to investigate whether the observed decreased prevalence of coronary artery disease in individuals with Down's syndrome may be explained by their serum lipid and lipoprotein profiles. Twenty-seven persons with Down's syndrome and 23 non-affected control individuals were enrolled in this study. Their fasting venous blood was analysed for total cholesterol, triglyceride, LDH cholesterol, HDL cholesterol, apo B and apo AI. The results revealed no significant differences between the study and control group with regard to total cholesterol, LDL cholesterol, apo B and the apo B:apo AI ratio. However, triglyceride levels were significantly increased, and serum HDL cholesterol, apo AI and HDL cholesterol:total cholesterol ratio were significantly decreased in patients with Down's syndrome when compared with the control group. The latter observations are all associated with an increased risk for coronary artery disease. Therefore, it is concluded that the decreased prevalence of coronary artery disease in individuals with Down's syndrome cannot be explained by the lipid and lipoprotein levels observed in this study population.