A group of eight synthetic peptides, corresponding in sequence to selected regions of HLA-DQ histocompatibility antigens, was used for rabbit immunization to examine their antigenicity and for localizing exposed regions in the native glycoproteins. Those antibodies were then tested in their ability to recognize the HLA-DQ alloantigens. Seven peptides elicited rabbit antibodies, four of which reacted with human glycoproteins prepared from chronic lymphocytic leukaemia cells. The results indicate that sequence stretches 63 to 79 and probably 82 to 93 of the beta chain correspond to exposed regions in DQw1, DQw2 and DQw3 molecules. However, the specificity of those antipeptide antibodies was low, due to extensive crossreactions with amino acid sequencies of high homology occurring in DQ alloantigens.