Previous studies have suggested that MHC class II polymorphism can influence the recognition of retroviral superantigen by murine T cells that have an intrinsically weak avidity for the superantigen. The aim of the present study was to determine whether bacterial superantigen recognition also is influenced by MHC polymorphism. Therefore, we screened for TCR with a low avidity for the bacterial superantigen SEB, and identified two V beta elements (V beta 14 and V beta 16) that had not been associated previously with SEB recognition. This finding extends the number of previously identified SEB-reactive V beta elements (V beta 6, V beta 7, V beta 8.1, V beta 8.2, and V beta 8.3) to at least seven. A detailed comparison of SEB recognition by V beta 14+ and V beta 8.2+ T cell hybridomas revealed two interesting features. First, SEB recognition by V beta 14+ hybridomas was relatively weak compared with V beta 8.2+ hybridomas. Second, in contrast to V beta 8.2+ hybridomas, individual V beta 14+ hybridomas responded differentially to SEB presented by either I-Ed or I-Ek molecules on the surface of L cell transfectants, indicating a role for polymorphic residues of the MHC in superantigen presentation. These findings demonstrate that T cell recognition of bacterial superantigens can be influenced by MHC polymorphism in a manner analogous to that of retroviral superantigen recognition, and that this characteristic is a feature of low avidity T cells. Taken together, these data support the hypothesis that there is a direct interaction between the TCR and MHC molecules during superantigen recognition.