The test substance, preferably radiolabelled, is applied, for a fixed period of time, to the clipped skin of animals at one or more appropriate dose levels in the form of a representative in-use preparation. The rat is the most commonly used species. At least four animals of one sex should be used for each test preparation and each scheduled termination time. A known amount of the test preparation is evenly applied to the site. This amount should normally mimic potential human exposure, typically 1-5 mg/cm for a solid or up to 10 l/cm for liquids. A relevant exposure period (typically 6 or 24 hours) should be used, based on the expected human exposure duration. The animals should be observed for signs of toxicity/abnormal reactions at intervals for the entire duration of the study. This study includes: daily measurements (excreta), regular detailed observations, as well as sacrifice at the scheduled time and blood collected for analysis.