Avidin from egg white was migrated toward a cathode of nondenaturing electrophoresis and then immobilized on a polyvinylidene difluoride membrane. Adrenocorticotropic hormone (ACTH) was specifically captured after the biotinylated anti-ACTH antibody was bound to the membrane-immobilized avidin, and the captured ACTH was digested by the biotinylated trypsin on the membrane after extraction. The digested polypeptides from the ACTH were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). These results indicate that target substances can be specifically trapped and digested on membrane-immobilized avidin. (C) 2011 Elsevier Inc. All rights reserved.