The Stanford Coronary Risk Intervention Project was a four-year randomized clinical trial that showed that risk reduction through lifestyle change and lipid-lowering medications significantly reduced the rate of narrowing of the minimum diameter of coronary artery segments with angiographically visible lesions in 119 patients versus 127 controls who received usual physician care. In collaboration with this trial, Dr. Ronald Krauss measured high-density lipoprotein (HDL) subclasses by gradient gel electrophoresis. HDL may be divided into two HDL2 and three HDL3 subclasses that are approximated by their estimated particle diameters: HDL3c (7.2-7.8 nm), HDL3b (7.8-8.2 nm), HDL3a (8.2- 8.8 nm), HDL2a (8.8-9.7 nm) and HDL2b (9.7-12.9 nm). The HDL- distribution can also be characterized by the diameter of the predominant peak, which may lie in either the HDL3b or HDL3a interval. Case control and angiographic studies suggest that coronary heart disease risk is increased when HDL2b is reduced relative to HDL3c and HDL3b. See also Study 27.