Forty-three patients were studied to determine whether light chain gene rearrangements may occur in hematopoietic cells not pertaining to the B-lineage. In only one patient, affected by T-cell lymphoblastic lymphoma, one kappa light chain allele was rearranged. Neither at the protein level nor at the RNA level the rearranged gene was expressed. These data confirm that, although rarely, kappa light chain gene rearrangements may occur in neoplastic T-cells. Furthermore, as in our patient Ig heavy chain genes retained a germline configuration, the present data demonstrate that kappa light chain gene rearrangements may occur regardless of Ig heavy chain gene arrangement.