Murine T cells carry either of two antigen receptors on their surface: alpha beta or gamma delta T-cell receptors (TCR). The function of gamma delta T cells is not well understood. In this population, subsets exist with tissue-specific localization, with invariant variable regions, and with specificity for self antigens. We have analyzed the murine TCR gamma locus by field inversion gel electrophoresis and cosmid cloning. The structure of the complete TCR gamma locus, the first complete physical map of any mouse TCR locus, is reported here. The locus spans 205 kb and consists of four clusters of genes and gene segments. Each cluster contains one or more variable elements, one joining element, and one constant element. We demonstrate that the C gamma 4 gene is distinguished from the other C gamma genes in that it has an additional hinge-encoding exon. New enhancer-like elements are identified in two of the clusters, downstream from the C gamma genes. The most upstream cluster has four V elements and resembles the human TCR gamma locus. The four clusters probably arose via duplications.