The discovery of the potent mutagenicity of AF-2, which was once used in Japan as a food preservative, has exerted a great influence not only on screening procedures for carcinogenic compounds but also on legislative approaches to mutagenic substances. It promoted the synthesis of exceedingly sensitive and reliable tester strains in Salmonella and supported the hypothesis of a common mechanism between mutagenicity and carcinogenicity. Thus preliminary screening for carcinogenic substances has become feasible using mutagenicity as an index. It also contributed greatly to the formulation of legislative measures for chemical substances which for the first time gave due attention to mutagenicity. Furthermore, the exposure of a large population to such a potent mutagen raised a question as to what extent the genetic constitution of the Japanese population might have been damaged. This suggested that urgent need for a system to monitor the total genetic damage to a human genome.