B‐cell chronic lymphocytic leukemia (B‐CLL) is characterized by the accumulation of mature‐appearing clonal B cells exhibiting coexpression of CD5 and CD23. In addition to the accumulation of neoplastic B cells, numerous T‐cell abnormalities also occur in B‐CLL patients. In this study, the presence, and distribution within the T‐cell subsets, of clonal/oligoclonal T cells was studied. Multicolor flow cytometric techniques were employed using combinations of anti‐CD3, anti‐CD4, and anti‐CD8 antibodies coupled with antibodies specific for V_α and V_β T‐cell receptor (TCR) epitopes. Molecular studies of TCR gene sequences were done to confirm the presence of clonal/oligoclonal T‐cell populations. In the flow cytometric studies, examination of V_α/V_βexpression found evidence of clonal/oligoclonal expansion in 9 of 19 patients studied. In eight of the nine patients, the expansions were restricted to the CD3⁺CD8⁺ cell population. Molecular analyses were performed in 16 patients, 12 of whom showed a clonal or oligoclonal pattern. Of the four patients who were negative in the molecular analyses, all demonstrated flow cytometric evidence of clonal/oligoclonal expansions. Thus, when the flow cytometric and molecular analyses were considered together, all 16 patients for whom parallel analyses were done showed evidence of clonal/oligoclonal expansions. These results confirm previous work demonstrating that the majority of B‐CLL patients harbor clonal/oligoclonal expansions within the T‐cell population. Additionally, based on the relative numbers of cells expressing specific V_α or V_βepitopes, these results show that these expansions occur primarily within the CD3⁺CD8⁺ T‐cell population. Cytometry (Comm. Clin. Cytometry) 42:188–195, 2000. © 2000 Wiley‐Liss, Inc.