Monoclonal expansions of immunoglobulin (Ig) and T-cell receptor (TCR) genes are, respectively, important markers for B- and T-cell malignancies. We used BIOMED-2 protocols to detect clonality of these genes in B- (BCL) and T-cell lymphoma (TCL) in southern Taiwan. Heteroduplex analysis was used after PCR reactions. Ig/TCR clonality rates were 95% (22 in 23 cases) for BCL and 76% (19 in 25 cases) for TCL. These results reveal overall satisfactory detection rates for both BCL and TCL. None of the four natural killer (NK)/T-cell lymphomas detected showed TCR gene clonality, which suggested that BIOMED-2 protocols distinguished the NK/T-cell lymphoma from TCL. In addition, three of the five tested precursor T-cell lymphoblastic lymphomas showed no TCR gene clonality, probably because the immature T-cells in this type of TCL had not undergone TCR gene rearrangements. We conclude that BIOMED-2 protocols are suitable for detecting Ig and TCR clonalities in B- and T-cell malignancies in southern Taiwan.