Determination of the T cell receptor Vbeta repertoire of human CD4 and CD8 populations is a useful immunological tool, particularly in the investigation of superantigen involvement in various disease states. We describe the optimisation of a rapid technique for the simultaneous evaluation of 24 Vbeta families of the T cell receptor of CD4 and CD8 positive lymphocytes in whole blood by flow cytometry adapting a commercially available monoclonal antibody kit. The technique described is reliable and reproducible, and we describe its use as a potential diagnostic tool in patients with staphylococcal and streptococcal toxic shock syndromes.