The accurate measurement of T-cell receptor (TCR) repertoire changes requires the analysis of a representative sampling of complex T-cell populations. The number and frequency of clonally expanded TCR beta-chain transcripts bearing distinct CDR3 sequences were accurately determined using a simple DNA heteroduplex tracking assay. This method allowed major and minor clonal expansions (> or = 1% of a Vbeta subfamily's transcripts) to be rapidly and reproducibly quantified. Oligoclonal CD8 + cell expansions were detected in all young adults tested, while CD4 + cells generally expressed more polyclonal beta-chain repertoires. The same pattern of CD8 + cells oligoclonality and CD4 + cells polyclonality was observed in asymptomatic HIV-1 infected individuals with high CD4 + cell counts. CD8 + CD45RA + and CD8 + CD45RO + cell fractions both displayed oligoclonal, although distinct, TCR beta chain repertoires while CD8 + cells from umbilical cord blood were generally polyclonal. Oligoclonal CD8 + cell repertoires from young adults were generally stable over a period of weeks, although minor, transient, clonal expansions could also be detected in the absence of symptomatic infections. DNA heteroduplex tracking analysis provided a higher level of sensitivity for the detection of TCR beta chain transcript expansions than CDR3 length (spectrotyping/immunoscope) analysis. DNA heteroduplex tracking of TCR beta-chain transcripts is therefore a simple and sensitive method for assessing the level of clonality and for measuring changes in the TCR beta chain repertoire of different T-cell populations.