Gene expression analysis of the T cell receptor repertoire can provide useful information in evaluating the immune response in a variety of conditions. TCR spectratyping is a multiplex RT-PCR protocol used to analyze the T cell repertoire diversity by comparing the relative frequencies of different clonal length products within the CDR3 region of a particular TCR Vβ family. This technique is useful for analysis of clonal compositions in T cell populations, which changes during an immune reaction and can be dramatically altered in some disease states. This assay provides qualitative information regarding the diversity of the TCR Vβ repertoire but for quantitative information, the flow cytometric Vβ repertoire analysis needs to be used.