Previous studies have shown that the receptor for quinine- and quinidine-dependent antibodies is not expressed on the surface of platelets from patients with the Bernard-Soulier (B-S) syndrome. We now report data to suggest that these platelets lack the receptor for these antibodies. Since B-S platelets are also missing 2 related components of the GP I complex, GP lb and glycocalicin, our findings suggest that the receptor for quinine- and quinidine-dependent antibodies may be associated with this complex on normal platelets. An antibody previously shown to be directed against a surface antigen that migrated in the GP I position on SDS-polyacrylamide gel electrophoresis specifically blocked the reaction of the receptor with quinine- or quinidine-dependent antibodies. Purified glycocalicin, however, lacked detectable receptor activity. In contrast, a mixture of GP lb and a putative structural analog of this glycoprotein (Mr 210,000) eluted from wheat germ affinity columns after chromatography of Triton X soluble preparations of platelets or membranes was shown to contain at least 80% of the total receptor activity. Our results strongly suggest that the receptor is associated with GP lb and/or its high m.w. structural analog(s).