A Balb/c mouse was immunized with chick synaptic plasma membranes and monoclonal antibodies were produced by fusion of spleen cells with NS-1 mouse myeloma cells. One antibody, MAC-L1, immunoprecipitated more than 90% of the [3H]PN200-110-labeled calcium channels but only 20% of the omega -conotoxin receptor solubilized from the chick brain membranes. Thus possibly, a certain portion of the omega -conotoxin receptor in the chick brain is a dihydropyridine-sensitive calcium channel. By the specific immunoprecipitation of 125I-labeled proteins, two large polypeptides of 193kDa and 130kDa under reducing conditions were identified as the major components of the calcium channel.