A monoclonal antibody (mAb) was developed which precipitated kainate binding activity from detergent extract of pigeon cerebellum and was used to isolate a kainate binding protein (KBP) by immunoaffinity chromatography. It migrated at an apparent molecular weight (Mr) of 220,000 in gel filtration chromatography and at Mr = 50,000 in polyacrylamide gel electrophoresis performed under denaturing and reducing conditions. Moreover, the mAb produced an immunohistochemical staining pattern in the molecular and Purkinje cell layers which corresponded to the autoradiographic labeling pattern observed with tritiated kainate and were reported to be typical of the major kainate binding site in the pigeon cerebellum.