The thiazolidinediones are a new class of compounds approved for the treatment of type 2 diabetes. Because these drugs directly improve insulin resistance and decrease plasma insulin concentration, they have the potential to decrease the risk for cardiovascular disease in diabetic patients. A number of studies have demonstrated changes in several cardiovascular risk factors associated with the in-sulin resistance syndrome. These effects include decreasing of blood pressure, correcting diabetic dyslipidemia, improving fibrinolysis, and decreasing carotid artery intima-medial thickness. Other in vitro effects related to their ability to bind a newly described class of receptors (peroxisome proliferator-activated receptors) may also have implications for atherosclerosis. Although these drugs increase low-density lipoprotein (LDL) cholesterol, they induce a favorable change in the LDL particle size and susceptibility to oxidation. The implications of these changes are not clear. Because of their mechanism of action, clinical trials have been designed to determine whether these drugs (or similar insulin sensitizers) will decrease cardiovascular events in people with type 2 diabetes.