Southern blot and polymerase chain reaction (PCR) were used to analyse rearrangements of antigen receptor genes in 27 cases (fresh tissues) and 51 cases (paraffin-embedded specimens) of non-Hodgkin's lymphomas (NHL). Thirty in 31 cases of NHL detected by Southern blotting showed IgH and/or IgK and/or TCR beta gene rearrangements. Of NHL with T-cell phenotype, 12 of 14 cases presented rearrangement of TCR beta gene. All the cases of analysed B-cell lymphomas displayed rearrangements of IgH and/or IgK genes. Two cases of NHL were considered bi-genotypic. Both showed IgH and TCR beta gene rearrangements. Three cases unclassified with immunophenotyping showed IgH and/or IgK gene rearrangements. In contract to the above findings all cases of reactive lymphoid hyperplasias demonstrated a germline configuration of antigen receptor genes, PCR analysis showed that monoclonal bands were observed in 77% of B-NHLs with IgH primers and 91% of T-cell lymphomas with TCR gamma primers. Besides, 4 cases of "borderline" lymphoid hyperplasias showed clonal bands of IgH and/or TCR gene rearrangements. The results suggested that gene rearrangements of antigen receptors is one of the most sensitive and valuable clonal markers in the diagnosis of lymphomas, and an important supplement to morphological diagnosis and immunophenotyping.