The objective of this document is to provide guidance on how to derive an Acute Reference Dose (ARfD). It outlines a stepwise approach on how to best use all available toxicological data, and what to do if more data are needed on the refinement of the toxicological data base with regard to the acute effects of the compound being investigated or an advanced exposure assessment, if the risk assessment indicates a human health concern. This guidance document is primarily intended for pesticides, biocides and veterinary drugs, but could be used for all categories of chemical substances which may be ingested by human beings in food and/or drinking water as well as non-dietary oral exposure. The general principles and concepts can also be applied to dermal and inhalation exposure routes. However, these routes would more appropriately be addressed in separate OECD guidance documents.