Gene rearrangement and monoclonality have been detected in non-Hodgkin's lymphomas (NHLs). The semi-nested polymerase chain reaction (PCR) was performed to amplify IgH and the mixed PCR to TCR gamma gene rearrangements. Monoclonal band was observed in 77% of B-cell NHLs with IgH primers and 91% of T-cell NHLs with TCR gamma primers. The results show that PCR is more valuable in determining the clonality and lineage of the tumor. Moreover, 3 cases of "borderline" lymphoid hyperplasia showed clonal bands of IgH and TCR gamma gene rearrangements and follow-up studies found that one patient died of the disease 13 months after biopsy. Presumably, gene rearrangement analysis plays a significant role in the discovery of early stage disease. In comparison with Southern blot, PCR is simple, more convenient and rapid. Furthermore, no isotope is required and can be used in paraffin embedded sections, cytologic specimens and other materials. This technique can therefore be used in daily clinical diagnosis.