Strong evidence exists for adaptation to heavy metals, i.e. cadmium and lead, in populations of the soil arthropod O. cincta from heavy metal contaminated sites. A cadmium binding metallothionein (mt) was isolated, which is significantly higher expressed in a population from an old Pb-Zn mine, compared to a control population. Previous research suggested significant additive genetic variation for transcriptional regulation of the mt. Eight alleles of the promoter, 1.3 kb 5’ of the mt ORF, have been sequenced which differ in the number and the arrangement of transcription factor binding sites, such as metal responsive elements (MRE), antioxidant responsive element (ARE), molting hormone receptor sites. The dose-response relationship by heavy metals, oxidative stress and 20-hydroxyecdysone on the induction of these promoter alleles was analyzed in a luciferase reporter assay in an insect cell line. Striking differences in inducibility by Cd and oxidative stress (paraquat) were detected and allele frequencies in a preliminary field study suggest a combination of balancing and positive selection in a metal polluted environment.