Immunochemical techniques for the study of acetylcholine receptors are described. Immunization of rabbits, rats, guinea pigs, and goats with acetylcholine receptor protein purified from Electrophorus electric organ tissue results in muscular weakness and death due to impaired neuromuscular transmission. Serum from immunized animals contains high concentrations of antibodies directed at receptors from the electric organ and low concentrations of antibodies directed at receptors from skeletal muscle. The detailed similarities between the disease of receptor-immunized animals "experimental autoimmune myasthenia gravis" (EAMG), and myasthenia gravis are compared. Reactions of antisera from animals with EAMG with receptor from Electrophorus and Torpedo are studied. Antireceptor antibodies in these antisera are directed predominantly and determinants other than the acetylcholine-binding site.