It has been recognized that clonal T-cell receptor delta (TCRG) gene rearrangement is present in both Tand B-cell malignancies. The highly sensitive polymerase chain reaction (PCR) technique may be applicable to cases of leukemia and lymphoma of non-T-cell origin for detection of minimal residual disease (MRD). A PCR technique was used in this study to investigate the pattern of clonal TCRG gene rearrangement in Hong Kong Chinese patients with non-T-cell hematological malignancies. Seventy-three patients with the diagnosis of acute leukemia and non-Hodgkin's lymphoma of non-T-cell origin were included in this study. There were 20 patients with common ALL (CALL), seven precursal B-cell ALL (PreB-ALL), 23 acute myeloid leukemia (AML), and 23 non-Hodgkin's lymphoma of B-lineage (B-NHL). Clonal rearrangement was detectable by Southern analysis using a JG1 probe in 41 per cent of ALL of B-lineage but in none of the B-NHL or AML. The samples were also studied further by monoclonal PCR amplification for TCRG gene rearrangement. Three different sets of primers were employed to detect clonal rearrangement of the TCRG gene. The VGl(D)JGl recombination typically seen in T-cell malignancies were not seen in any of the of the non-T-cell malignancies. The V62(D)D63 recombination was found exclusively in ALL of B-lineage and was seen in 73 per cent of the Southern positive cases. Although clonal TCRG gene rearrangement was undetectable by Southern analysis in our AML cases, 26 per cent had a V62(D)JG1 recombination found by the PCR technique. Sensitivity of the PCR technique was determined by serial mixing and was up to 5-10 leukemic cells per lo4 nucleated cells. It was apparent from this study that it was feasible to detect clonal TCRG gene rearrangement by the PCR technique in a proportion of the cases of non-T-cell hematological malignancies. The PCR technique can be applied to detect residual leukemic cells in marrow of patients in an apparent morphological complete remission. The value of this application requires further clinical evaluation and correlation.