A major characteristic of superantigens is their ability to stimulate T cells based predominantly on the type of variable segment of the T-cell receptor (TCR) V beta chain. Recently, however, reports from several laboratories have also implied a role for non-V beta elements in superantigen binding. The goal of the present study was to determine whether TCR V beta-D beta-J beta joining sequences may influence the interaction of superantigens with their target cells. To ascertain how the actual TCR repertoire of superantigen-triggered cells deviates from the theoretical one, we generated a large panel of joining region sequences from TCR carrying the TCR V beta 12 and TCR V beta 5,1 regions. The 245 sequences analysed represent transcripts of T cells from the same donor triggered either with an anti-CD3 monoclonal antibody or with the Staphylococcus aureus enterotoxins. Comparison of the joining sequences of these different groups demonstrates a skewed J beta usage in the sequences derived from superantigen-triggered cells and also provides evidence that ascribes to the putative CDR3 region of V beta segments a role in superantigen recognition. Finally, the data presented give some hints of the regions of the putative CDR3 loop that may play a major role in this function.