Cayman's Lipid Hydroperoxide Assay measures the hydroperoxides directly utilizing the redox reactions with ferrous ions. An easy to use quantitative extraction method was developed to extract lipid hydroperoxides into chloroform, and the extract is directly used in the assay. This procedure eliminates any interference caused by hydrogen peroxide or endogenous ferric ions in the sample and provides a sensitive and reliable assay for lipid peroxidation. This kit is available in two formats: 100 dtn, which is designed to be read using a single-tube spectrophotometer, and 96-wells, which is designed to be read using a 96-well microplate reader. The 96-well kit contains a special glass plate which is resistant to organic solvents used in the assay; this is the only difference between the two kit types.