The murine lck gene is closely related to a family of cellular protooncogenes and encodes a lymphocyte-specific, membrane-associated protein tyrosine kinase. We and others have demonstrated that the lck gene is rearranged and overexpressed in the murine lymphoma LSTRA, most likely as a result of the insertion of Moloney murine leukemia virus DNA immediately adjacent to the gene. We now report that the lck gene is located at the distal end of murine chromosome 4 and on human chromosome 1 at position 1p32-35 near a site of frequent structural abnormalities in human lymphomas and neuroblastomas. These results raise the possibility that structural alteration of the lck gene through chromosomal rearrangement may contribute to transformation in human malignant disease.