The following parameters will be measured in blood samples collected from the VA-HIT study and the Framingham Offspring Study: apo A-I-containing HDL subspecies (prebeta, alpha, and prealpha) in plasma using two-dimensional gel electrophoresis immunoblot and image analysis, LpA-I and LpA-I/A-II in plasma using differential electroimmunoassay, and apo C-III in HDL using immunoturbidometric assay. The study hypotheses are as follow. a) Subjects from the placebo arm of VA-HIT will have significantly lower alpha l HDL subspecies, LpA-I, and apo C-III in HDL, and higher HDL/alpha l and apo A-I/alpha l ratios than subjects free of coronary heart disease from the Framingham Offspring Study. b) These parameters will also predict prospectively risk of coronary heart disease in both groups. c) In the VA-HIT study, treatment with gemfibrozil, which has been shown to be associated with a 22 percent reduction in myocardial infarction and coronary heart disease death, will be associated with increases in alpha l HDL subspecies, LpA-I, and apo C-III in HDL, as well as decreases in HDL/alpha l and apo A-I/alpha l ratios, compared to placebo. d) The hypothesis that subjects with specific mutations in the lipoprotein lipase gene have less beneficial changes in HDL subspecies with gemfibrozil than subjects with no mutations will also be tested.