To identify axonal proteins which are unique constituents of neurons, the spectrum of detectable proteins of degenerating nerves has been compared with that of intact control nerves from the same animals. Wallerian degeneration was induced in rabbits by unilateral transection of the optic and sciatic nerves. Proteins of nerve homogenates were compared by sodium dodecyl sulfate-gel electrophoresis and by two- dimensional electrophoresis. Four non-myelin proteins disappear from degenerating nerve. These include the three neurofilament proteins (P68, P150, and P200) and a polypeptide with a molecular weight of about 65,000 daltons (P65) which is not associated with filaments.