Although the T cell gamma genes are similar in many respects to T cell receptor alpha and beta genes, earlier studies suggested that only a single gamma variable (V gamma) gene is expressed in mature T cells. We report the isolation and characterization of three new rearranged V gamma genes from murine fetal thymocytes. Although each of the new V gamma gene rearrangements is present in fetal thymocytes, two of them are undetectable in mature T cells. The levels of mRNA corresponding to each type of V gamma gene rearrangement in mature T cells are dramatically diminished compared with those in fetal thymocytes, although the abundance of two of the rearranged genes is increased in mature T cells. Our results demonstrate that there is significant expressed variability of gamma genes in immature T cells. Furthermore, the dynamics of gamma gene rearrangement and expression support the idea that gamma genes function in immature T cells.