The distribution of coenzyme Q(10) (CoQ(10)) in serum lipoprotein fractions was measured by high-speed liquid chromatography during myocardial infarction and cerebral infarction. In control subjects, the major part of CoQ(10) was present in the LDL fraction, and the distribution of CoQ(10) was correlated with that of cholesterol. The CoQ(10) level was related to the phenotypes of hyperlipidemias: more CoQ(10) was present in LDL in type Ⅱa, and in VLDL in types Ⅱb and Ⅳ. In myocardial infarctions, the CoQ(10) concentration decreased on the 3rd day, then gradually returned to the initial level in the serum and LDL fraction, while it decreased gradually untill the 21st day in the HDL fraction. The CO(10)-cholesterol ratio decreased on the 3rd day in serum, and on the 3rd, 7th and 14th days in the LDL fraction. In contrast, there was no significant change in the HDL fraction. In cerebral infarctions, the CoQ(10) concentration decreased on the 3rd and 7th days in serum, and on the 3rd day in the HDL fraction. These results suggest that part of the metabolism of CoQ(10) is the same as that of cholesterol in serum lipoproteins, and that CoQ(10) is carried from LDL and HDL to mitochondria-rich organs during repair.