Antigen recognition by αβ T lymphocytes is mediated via the multisubunit TCR complex consisting of invariant CD3γ,δ,ε and ζ chains associated with clonotypic TCRα and β molecules. Charged amino acids located centrally within the TCRα transmembrane region are necessary and sufficient for assembly with the CD3δε heterodimer. Previously, we have shown that deletion of 6–12 amino acids from the carboxy terminus of the TCRα-chain dramatically abrogates surface TCR expression, suggesting that the distal portion of the TCRα transmembrane region contains information that regulates the assembly and/or intracellular transport of TCR complexes. We have examined in more detail the molecular basis for reduced TCR expression in T cells bearing truncated TCRα chains. We found that in contrast to wild-type (wt), variant TCRα proteins missing the last nine C-terminal amino acids did not associate with core CD3γ,δ,ε chains and were not assembled into disulphide-linked αβ heterodimers. The stability of newly synthesised wt and variant TCRα molecules was similar, showing that the abrogated surface TCR expression was not a consequence of impaired protein survival. Nevertheless, truncated TCRα chains still assembled with the chaperon protein calnexin in the endoplasmic reticulum, indicating that the distal portion of the TCRα transmembrane region is not essential for calnexin interaction. These data document a role for the distal portion of the TCRα transmembrane region in the assembly of TCR complexes and provide a molecular basis for reduced TCR expression in cells bearing truncated TCRα chains.