At the present time there are four intense sweeteners that are available in a number of countries: acesulfame-K, aspartame, cyclamate and saccharin. Extensive toxicity databases are available on each sweetener and these have been assessed by both national and international regulatory authorities. This review considers briefly the critical toxicity of each sweetener that is the basis for establishing the no adverse effect level in animal studies. The calculation of an acceptable daily intake (ADI) for human intake employs a large safety factor applied to the no-effect level. The magnitude of the safety factor for each sweetener is discussed in relation to the ADI values recommended by the Scientific Committee for Food in 1985.