Due to the physiological importance of its product, the Cu/Zn superoxide dismutase enzyme, the gene coding for this enzyme was mapped in five species of the Drosophila willistoni subgroup and in D. nebulosa by in situ hybridization using D. melanogaster as a control. The results indicate that this locus is located on the XR chromosomal arm of the five sibling species and on the XL chromosomal arm of D. nebulosa, suggesting the occurrence of a pericentric inversion before the separation of these entities.