Gene rearrangement analysis using Southern-blot hybridization technique is a standard method for evaluating clonal receptor gene rearrangement. Both clonality and lineage can be identified in lymphoid neoplasms by the demonstration of one or more rearranged antigen receptor genes of the immunoglobulin supergene family-immunoglobulin and T-cell receptor genes. To evaluate the diagnostic applicability of antigen receptor gene rearrangements in the diagnosis of malignant lymphomas and leukemias, the authors performed a gene rearrangement analysis of 54 cases by southern blot hybridization technique. One or two clonally rearranged bands were detected in the malignant lymphomas and in the lymphoblastic leukemias with a false-negative rate of 13.8%. No clonal, rearranged band was detected in benign reactive hyperplasias, carcinomas or non-lymphocytic leukemias. Rearrangement analysis could resolve the lineage, clonality and stage of differentiation of malignant lymphoid neoplasms.