This Test method has been designed to provide information on absorption of a test substance, (ideally radiolabelled), applied to the surface of a skin sample separating the two chambers (a donor chamber and a receptor chamber) of a diffusion cell. Static and flow-through diffusion cells are both acceptable. Skin from human or animal sources can be used. Although viable skin is preferred, non-viable skin can also be used. The skin has been shown to have the capability to metabolise some chemicals during percutaneous absorption. In this case, metabolites of the test chemical may be analysed by appropriate methods. Normally more than one concentration of the test substance is used in typical formulations, spanning the realistic range of potential human exposures. The application should mimic human exposure, normally 1-5 mg/cm2 of skin for a solid and up to 10 µl/cm2 for liquids. The temperature must be constant because it affects the passive diffusion of chemicals. The absorption of a test substance during a given time period (normally 24h) is measured by analysis of the receptor fluid and the distribution of the test substance chemical in the test system and the absorption profile with time should be presented.