Abstract: β-Bungarotoxin-binding sites exist in the presynaptic membrane of rat phrenic nerve with a relatively high density.The purified β-bungarotoxin-binding protein was obtained from rat diaphragm muscle by a few steps (including homogenization,detergent solubilizaton,ion exchange chromatography,lectin affinity chromatography and β-bungarotoxin affinity chromatography) with a total yield of 3%.The specific binding activity of the purified protein preparations was around 1 nmol/mg protein.The pattern of SDS discontinuous buffer system polyacrylamide gel electrophoresis of the final protein preparation showed that two peptides were co-purified and their molecular weights were 61 and 69 kD,respectively.