A series of 12 monoclonal antibodies has been prepared against crude or purified individual bovine neurofilament (NF) triplet proteins (designated as P68, P150, and P200). Six of the antibodies recognized unique determinants on individual NF subunits. The other six recognized shared determinants on at least two NF triplet proteins. Six of the antibodies recognized separated, immobilized individual NF in nitrocellulose paper. By the peroxidase-antiperoxidase technique, all of the antibodies stained neurons and their processes in a manner identical to the well-known distribution of NF in both the central and peripheral nervous system. These results strongly suggest that the NF subunits are distinct but related proteins and that the smaller NF subunits (P68 and P150) are not derived from larger NF proteins.