SIGNIFICANCE and RATIONALE: Low HDL cholesterol levels elevate CAD risk independent of low density lipoprotein (LDL) cholesterol levels. In association with high triglyceride levels and with small LDL particle size, low HDL is part of the syndrome of atherogenic dyslipidemia. This form of dyslipidemia is characteristic of the underlying dyslipidemia found in HIV-infected subjects, likely represents the consequences of chronic inflammatory changes due to HIV, and contributes substantively to the CAD risk in this population even without the added risk from dyslipidemic antiretroviral medications. Primary CAD preventive modalities may be warranted for patients in the HIV population as well as in the general population who manifest this type of dyslipidemia. Niacin is currently the best medication available to elevate HDL cholesterol levels. Thus, using the novel technique of assessing flow-mediated dilatation of the brachial artery, a pilot project is proposed to assess whether the use of extended release niacin will lead to short term improvement in endothelial function. If successful, this study may lay the foundation for further studies into the potential use of niacin for prevention of CAD in patients who are particularly at risk for CAD due to low HDL cholesterol levels.