Abstract: Tetrahymena pyriformis cells were first cultured in a proper medium in which R. E. tracer Ce-141, or Yb-169, or Tin-170 was spiked. It was assayed that 65% of the radioactivity localized in the cell pellicle. By a biochemical centrifuging procedure, pellicle was isolated from cilia, mitochondria etc……Membrane protein was extracted with a detergent, 2% sodium deoxycholate The compatible overlap of a protein elution peak and a radioactivity elution peak of the Sephadex G-100 gel chromatogram demonstrated the existanee of a R E. binding protein. By means of SDS-polyacrylamidegel electrophoresis a molecular weight of 54000 daltons of the protein was determined when compared with standard proteins.