We evaluated the importance of CD3-ζ ITAMs in T cell responses by breeding the P14 transgenic TCR into mice in which CD3-ζ chains lacking all or part of their ITAMs were genetically substituted for wild-type CD3-ζ chains. In contrast to the H-Y TCR, the P14 TCR permitted the development of peripheral CD8⁺ T cells harboring signaling-defective CD3-ζ subunits. The absence of functional CD3-ζ ITAMs did not reduce the spectrum of activation events and effector functions that constitute the normal attributes of mature CD8⁺ T cells. The only detectable differences were quantitative and noted only when T cells were challenged with suboptimal peptide concentrations. Therefore, the ITAMs present in the CD3-γδε module are sufficient for qualitatively normal TCR signaling and those present in CD3-ζ have no exclusive role during T cell activation.