To predict internal metal concentrations in animals under specific environmental exposures, the relationship between the exposure concentrations and values of toxicokinetic parameters must be known. At high exposure levels, the availability of carriers transporting metal ions through cellular membranes may become limited, thereby decreasing the assimilation rates (k_A ). Furthermore, increased metal concentrations in food may result in greater damage to the gut and reduce the assimilation efficiency and/or increase the elimination rate (k_E ). Therefore, k A should decrease and k E should increase with increasing metal concentrations. In fact, our study on Tribolium castaneum exposed to Cu at 500, 1000, 2000 and 4000 mg kg^-1 of dry flour showed that with increasing Cu concentrations, k_A decreased from 0.0042 day^-1 at 500 mg kg^-1 to 0.0026 day^-1 at 4000 mg kg^-1 in females and from 0.0029 to 0.001 day^-1 in males and k_E increased from 0.027 to 0.064 day^-1 and from 0.018 to 0.04 day^-1 in females and males, respectively. Significant differences in k_A between the sexes were observed at 2000 and 4000 mg kg^-1, whereas significant differences between treatments were found for k_A in males. Copper was efficiently regulated by T. castaneum: an eightfold increase in exposure concentrations resulted in only a ca. twofold increase in the internal concentration. No Cu effect on the respiratory metabolism of T. castaneum was found.