Abstract:Gene rearrangements of immunoglobulin and T cell antigen receptor gene loci were studied in 67 patients referred to a general hematology clinic. The results of gene analysis supported the clinical diagnosis in most cases where involved tissue was studied. However, in a number of cases, gene rearrangement studies gave unexpected results of possible diagnostic significance. Thus two patients who presented diagnostic difficulties were finally diagnosed as having non‐Hodgkin's lymphoma; gene analysis suggested that the initial diagnosis of Hodgkin's disease may have been correct. In two patients who had chronic lymphocytosis and were suspected of having chronic lymphocytic leukemia, no evidence of monoclonal disease of B or T cells could be found and the basis for the lymphocytosis was presumed to be non‐malignant. Gene analysis was able to detect monoclonal B cell disease in the otherwise normal blood of two of six patients with lymphoma, one of two patients with macroglobulinemia, and none of six patients with myeloma.The study of gene rearrangements may be a practical aid to diagnosis in some situations of uncertai