The development of kainate binding proteins in membrane preparations of chick cerebellum was studied with the novel photoaffinity ligand [3H] (2S.3S.4S)-4-[1-(4-azidobenzamidomethylethenyl)-2-carboxy-3-pyr rolidineacetic acid (ABCPA). Electrophoretic analysis revealed two major radioactive bands with apparent molecular masses of 45 and 33.5 kDa and pharmacological characteristics of high (45 kDa) and low (33.5 kDa) affinity kainate binding sites. The 33.5 kDa polypeptide is present already at embryonic day (E) 13, and the amount of incorporated radioactivity remains practically constant until post-hatching day (P) 48. In contrast, the 45 kDa polypeptide is undetectable at E13. Its appearance takes place at E17, and the amount of incorporated radioactivity dramatically increases until P6. Its developmental profile is identical to that observed for [3H] kainic acid reversible binding in the same tissue. It is suggested that the 33.5 kDa polypeptide, which appears in the early stages of development may participate in receptor complexes, which play an important role in developmental phenomena.