Compounds of nickel, cadmium, cobalt and arsenic have been shown previously to inhibit DNA repair processes at low concentrations. In the present study we investigated whether this repair inhibition may be caused by the displacement of zinc in zinc finger structures of DNA repair proteins. As models, the bacterial formamidopyrimidine-DNA glycosylase (Fpg) and the mammalian XPA protein were applied. Both proteins were inhibited by Cd(II) and Cu(II). Hg(II) strongly inhibited the Fpg protein, but did not affect the XPA protein. In contrast, the XPA protein was disturbed by Co(II) and Ni(II), while the activity of the Fpg protein was not reduced. Neither protein was inhibited by As(III) or Pb(II). Thus, each zinc finger protein appears to have its own structural features and sensitivities towards toxic metal ions. Furthermore, each metal exerts specific mechanisms leading to DNA repair inhibition.