The molecular mass distribution of various metals was evaluated in cell lysates obtained from liver and brain of mice using size-exclusion chromatography (Superdex-75) with ICP-MS detection. Free-living mice Mus spretus were collected in polluted and non-polluted sites from Doñana National Park (southwest Spain) and SEC(HPLC)-ICP-MS was used to generate element specific chromatograms for essential metals (Cu and Zn) as well as toxic metals and metalloids (Cd, As, Pb). Different molecular mass fractions containing Cu are remarkably abundant in liver from the specimens captured in the polluted area. The fraction of about 7 kDa is especially important since it matches with a metallothionein I standard. Zn and Cd chromatograms also show peaks with similar molecular mass, but lower intensity. Analogous chromatograms from the non-contaminated site show a considerable depletion of these metal-containing biomolecules possibly due to low contamination. Chromatograms from the liver of laboratory mice Mus musculus (genetically close to Mus spretus) were also obtained for comparison revealing a great similarity with non contaminated samples. On the other hand, metal profiles from brain extracts do not reflect significant differences between polluted and clean areas in comparison with those obtained from liver of Mus spretus. Finally, the daily in vivo subcutaneous administration of Cd aqueous solution to Mus musculus during 10 days resulted in great rise of a Cd-peak of 7 KDa in the extract from the liver extract that matches with the Cd-methallothionein standard. Other Cd-binding molecules with higher molecular mass are also bioinduced by Cd exposure that probably constitutes a protection mechanism against this toxic element. The application for the first time of this metallomic approach to free-living mouse Mus spretus provides promising results for environmental stress assessment.