A method has been devised for the electro-phoretic transfer of proteins from polyacrylamide gels to ni-trocellulose sheets. The method results in quantitative transfer of ribosomal proteins from gels containing urea. For sodium dodecyl sulfate gels, the original band pattern was obtained with no loss of resolution, but the transfer was not quantitative.The method allows detection of proteins by autoradiography and is simpler than conventional procedures. The immobilized proteins were detectable by immunological procedures. All additional binding capacity on the nitrocellulose was blocked with excess protein; then a specific antibody was bound and,finally, a second antibody directed against the first antibody.The second antibody was either radioactively labeled or con-jugated to fluorescein or to peroxidase. The specific protein was then detected by either autoradiography, under UV light, or by the peroxidase reaction product, respectively. In the latter case,as little as 100 pg of protein was clearly detectable. It is antici-pated that the procedure will be applicable to analysis of a wide variety of proteins with specific reactions or ligands.