The intrinsic factor receptor, known to consist of two subunits alpha and beta, has been solubilized by papain digestion from porcine small intestine. Papain liberates a part of the outermost subunit (alpha) of the receptor. The solubilized part was called papain-alpha. It was purified by affinity chromatography on Sepharose-vitamin B-12-intrinsic factor gel and its molecular dimensions were measured. Its molecular weight measured with SDS-polyacrylamide gel electrophoresis is 45000, its isoelectric point is 4.2 and it binds the cobalamin-intrinsic factor complex in the same way as the whole receptor.