The T cell receptor (TCR)γδ and the pre-TCR promote survival and maturation of early thymocyte precursors. Whether these receptors also influence γδ versus αβ lineage determination is less clear. We show here that TCRγδ gene rearrangements are suppressed in TCRαβ transgenic mice when the TCRαβ is expressed early in T cell development. This situation offers the opportunity to examine the outcome of γδ versus αβ T lineage commitment when only the TCRαβ is expressed. We find that precursor thymocytes expressing TCRαβ not only mature in the αβ pathway as expected, but also as CD4⁻CD8⁻ T cells with properties of γδ lineage cells. In TCRαβ transgenic mice, in which the transgenic receptor is expressed relatively late, TCRγδ rearrangements occur normally such that TCRαβ⁺CD4⁻CD8⁻ cells co-express TCRγδ. The results support the notion that TCRαβ can substitute for TCRγδ to permit a γδ lineage choice and maturation in the γδ lineage. The findings could fit a model in which lineage commitment is determined before or independent of TCR gene rearrangement. However, these results could be compatible with a model in which distinct signals bias lineage choice and these signaling differences are not absolute or intrinsic to the specific TCR structure.