This is a report on our attempt to use polymerase chain reaction (PCR) to detect rearrangement of the immunoglobulin gene in the tissue specimens obtained from 30 patients with non-Hodgkin's lymphomas. There were 20 B-cell lymphomas and 10 T-cell. All 20 B-cell lymphomas but none of the 10 T-cell lymphomas had JH rearrangement by Southern analysis. Two pairs of primers (V670/OL-4 and VH26/OL-4) were designed to amplify the CDR3 region of the immunoglobulin gene heavy chain. The PCR analysis was positive using either one or both pairs of primers in 11 of the the 20 cases (55 per cent) of B-cell lymphomas which all had positive rearrangement by Southern analysis. The two pairs of primers seemed to produce complementary results as the specimens may be positive to one pair but negative to the other. The false negative rate of 45 per cent is however much higher than the respective figures of 18 per cent and 0 per cent observed in our patients with acute lymphoblastic leukemia and chronic lymphocytic leukemia in a previous study. Peripheral blood and bone marrow biopsy specimens obtained at the time of initial diagnosis were available from 10 patients with B-cell lymphomas whose lymph node biopsy specimens at the time of diagnosis were positive by both Southern analysis and PCR. All these peripheral blood and marrow specimens had no microscopic evidence of involvement by lymphoma cells and JH rearrangement was not detected by Southern analysis. However, rearranged bands identical to that of the lymph node biopsy specimen were detected by PCR in the peripheral and marrow blood of one of them. This PCR technique has been shown to have a sensitivity of 0.1 per cent in our previous report and may be more useful than morphology alone or Southern analysis in detecting minimal lymphomatous involvement in the peripheral blood and bone marrow at the time of initial diagnosis. Further clinical correlation is required to confirm the finding.