This review describes a procedure for the safety evaluation of flavouring substances. Over 2500 flavouring substances are currently in use in food. While toxicity data do not exist on all flavouring substances currently in use, within structurally related groups of flavouring substances many do have toxicity data and this information along with knowledge of structure-activity relationships and data on the daily intake provides a framework for safety evaluation. The safety evaluation procedure provides a scientifically based practical method of integrating data on intake, structure-activity relationships, metabolism and toxicity to evaluate flavouring substances in a timely manner. The procedure has been used recently by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) to evaluate a total of 263 flavouring substances.