The OECD Guidelines for the Testing of Chemicals are continually evolving to reflect changing assessment practices. Acute toxicity tests are an area of focus for developing alternative assays to address animal welfare concerns. In the context of this document, acute toxicity studies refer to studies involving a single exposure (i.e. a single exposure or multiple exposures within 24 hours) to a test chemical and include those assessing systemic toxicity as well as those assessing local irritation, corrosion or sensitization. One approach to minimizing the use of animals for acute toxicity testing is to consider waiving a study that may be required based on scientific criteria. These criteria include, but are not limited to, the consideration of physico-chemical properties of the test chemical or the potential for little or no exposure to that test chemical by a specific route. Another approach to reducing or eliminating animal testing is to use existing hazard information that is informative for the acute toxicity endpoint for the test chemical; this would include the use of hazard information for one or multiple similar test chemicals to characterize the hazard for another (often referred to as read-across) or for mixtures, the use of recognized calculation approaches and bridging concepts. Clarification of these approaches is important to ensure that regulatory authorities are provided with the appropriate data required for decision-making and that reduced animal testing can be undertaken without compromising the integrity of the hazard information.