In order to investigate the T-cell receptor (TCR) V beta usage in different T-cell subsets, the authors performed flow cytometric analyses using a large panel of TCR V beta-specific monoclonal antibodies on CD4+, CD8+ CD28+ and CD8+ CD28- T cells from 15 random blood donors, six umbilical cords and seven human leucocyte antigen (HLA) identical non-twin sibling pairs. The authors found that the proportion of T cells expressing each V beta gene product was similar within CD4+ and CD8+ CD28+ T cells from all samples studied. For these T-cell subsets a rank order of V beta usage could be identified which was adhered to by all donors. In contrast, within CD8+ CD28- T cells a wide variation of V beta usage was found between individuals, and no rank order correlation could be detected. Members of HLA identical sibling pairs were found to be no more similar in their usage of V beta gene products than pairs of HLA disparate random blood donors. Groups of individuals sharing HLA antigens were no different from the groups not sharing such antigens in their usage of V beta segments. The results suggest that HLA polymorphisms play no more than a minor part in determining TCR V beta usage.