The Comet assay, also called single cell gel electrophoresis, is a technique used for the sensitive detection of DNA damage in individual cells following exposure to a test compound. Electrophoresis is performed on exposed cells that have been embedded in agarose microgels. Damage resulting in DNA fragmentation is detectable by migration away from the nucleus. A DNA-stained damaged cell reveals the characteristic comet-like appearance: a bright ‘head’ (nucleus) and a ‘tail’ streak (damaged DNA). Types of damage measured include DNA strand breakage, DNA adducts, oxidative damage and cross-links. The length of the comet ‘tail’ and the intensity of DNA staining within it are proportional to the extent of DNA damage.