This Test Guideline describes an in vitro procedure that may be used for the hazard identification of irritant chemicals (substances and mixtures) in accordance with the UN Globally Harmonized System of Classification and Labelling (GHS) Category 2. It is based on reconstructed human epidermis (RhE), which in its overall design closely mimics the biochemical and physiological properties of the upper parts of the human skin. Cell viability is measured by enzymatic conversion of the vital dye MTT into a blue formazan salt that is quantitatively measured after extraction from tissues. Irritant test substances are identified by their ability to decrease cell viability below defined threshold levels (below or equal to 50% for UN GHS Category 2). Coloured chemicals can also be tested by used of an HPLC procedure. There are three validated test methods that adhere to this Test Guideline. Depending on the regulatory framework and the classification system in use, this procedure may be used to determine the skin irritancy of test substances as a stand-alone replacement test for in vivo skin irritation testing, or as a partial replacement test, within a tiered testing strategy.