Abstract: There are disclosed a process for detecting and determining an oxidized lipid in a specimen, which is capable of readily and accurately determining a specimen as containing an oxidized lipid, and a process for forming a water-soluble oxidized lipid having a hydroperoxide group which has specific influence on a living body. A specimen is detected and determined to contain an oxidized lipid by adding a lanthanide shift reagent to a specimen, followed by spectroscopic analysis thereof. An oxidized lipid is formed by adding superoxide dismutase (SOD) and CuSO.sub.4 to (1) an emulsion prepared by dissolving linoleic acid or arachidonic acid in deuterated methyl alcohol and adding the solution to a deuterated phosphate buffer under stirring, or to (2) a low density lipoprotein solution sufficiently dialyzed against an undeuterated phosphate buffer; followed by irradiation with long-wave ultraviolet light.