Day 14 fetal thymocytes and adult dendritic epidermal T cells (dEC) of all mouse strains express a characteristic non-polymorphic gamma delta T-cell receptor which is rarely found in the adult thymus or lymph nodes. We have made transgenic mice expressing this particular set of receptors on T cells in C3H and C57BL/6 mice. In adult mice of the latter strain, a dramatic depletion of transgene expressing T cells occurs and this effect is primarily mediated by thymic radiosensitive cells. The depletion is genetically dominant but not MHC-linked with major factor(s) mapping to chromosome 18. Taken together, our results show that strain-specific developmental changes in the thymic environment may play a role in shaping the gamma delta TCR repertoire.