The peptide‐binding properties of the nonclassical major histocompatibility complex (MHC) class 1b molecule Qa‐1 were investigated using a transfected hybrid molecule composed of the α1 and α2 domains of Qa‐1^b and the α3 domain of H‐2D^b. This allowed the use of a monoclonal antibody directed against H‐2D^b whilst retaining the peptide‐binding groove of Qa‐1^b. By comparison with classical MHC class I molecules, intracellular maturation of the chimeric molecule was inefficient with weak intracellular association with β2‐microglobulin. However, at the cell surface the hybrid molecules were stably associated with β2‐microglobulin and were recognized by cytotoxic T lymphocyte (CTL) clones specific for the Qa‐1^b ‐presented peptide Qdm (AMAPRTLLL). A whole‐cell binding assay was used to determine which residues of Qdm were important for binding to Qa‐1^b and CTL clones served to identify residues important for T cell recognition. Substitutions at position 1 and 5 did not reduce the efficiency of binding and had little effect on CTL recognition. In contrast, substitutions at position 9 resulted in loss of MHC class I binding. Mass spectrometric analysis of peptides eluted from immunopurified Qa‐1^b/D^b molecules indicated that Qdm was the dominant peptide. The closely related peptide, AMVPRTLLL, which is derived from the signal sequence of H‐2D^k, was also present, although it was considerably less abundant. The mass profile suggested the presence of additional peptides the majority of which consisted of eight to ten amino acid residues. Finally, the finding that a peptide derived from Klebsiella pneumoniae can bind raises the possibility that this non‐classical MHC class I molecule may play a role in the presentation of peptides of microorganisms.