With the exception of repair mutagenesis, which was reviewed two years ago (RHEASE, 3), the investigations of the basic molecular mechanisms of mutation induction by chemical substances seem to have reached a certain saturation level. The different types of mutations like transitions, transversions, deletions, frameshift mutations, backbone breakage, etc. have not been corrected, nor have new types of mutations been added in recent years. Therefore, the recent litarature on the molecular mechanism of mutation induction at the basic molecular level is rather limited.