We have mapped the chromosomal location of four genes previously assigned to human chromosome 21—Cu/Zn superoxide dismutase (SOD1), the protooncogene ETS2. the interferon α/β receptor gene (IFNAR), and the carbonyl reductase gene (CBR)—in the tammar. Macropus eugenii. The genes are localized on two separate autosomes: SOD1 and CBR map to chromosome 7 and ETS2 and IFNAR map to chromosome 3 or 4. These results provide the first example of asynteny between SOD1/CBR and ETS2/IFNAR in a mammalian species. The results suggest that either this synteny group has been disrupted in the marsupial lineage or, alternatively, the genes located on human chromosome 21 may have been joined after the marsupials diverged from the eutherian mammals some 130-150 million years ago.