A bacterial expression system was used to express the complete extracellular domain of a rat T-cell receptor alpha-chain, including variable-, joining and constant regions. By introduction of a His-tail at the C-terminus, a simple and rapid purification protocol utilizing Ni(+)-chelating chromatography was applied, with renaturation of the protein while bound to the matrix. This method produced large amounts of soluble protein, which provide a source for T-cell receptor analysis and further studies on T cell function.