Two-dimensional immunoblots revealed a spectrum of 200 kDa neurofilament polypeptides (Nf-H) of apparent molecular weights ranging from 200 to 170 kDa. The entire spectrum was stained immunocytochemically by three monoclonal antibodies specific for nonphosphorylated neurofilaments, while more restricted staining was revealed by four monoclonal antibodies specific for phosphorylated neurofilament epitopes. Treatment with increasing amounts of phosphatase suggested the existence of various forms of partially phosphorylated neurofilaments that possess phosphoepitopes that differ in their ease of dephosphorylation. Immunoprecipitation in low detergent concentration confirmed the existence of microheterogeneous forms of Nf-H that differed in extent of phosphorylation or in distribution of phosphorylated sites.