The present invention provides a soluble T cell receptor (sTCR), whichcomprises (i) all or part of a TCR .alpha. chain, except the transmembranedomain thereof, and (ii) all or part of a TCR .beta. chain, except thetransmembrane domain thereof. (i) and (ii) each comprise a functional variabledomain and at least a part of the constant domain of the TCR chain, and arelinked by a disulphide bond between constant domain residues which is notpresent in native TCR, characterised in that the sTCR recognises a CD1-antigencomplex, a bacterial superantigen or a peptide-MHC/superantigen complex.
