Abstract:Network of filaments, 10 nm in diameter, was detected in the frond cells of Adiantum philippense L. by selective extraction combined with whole mount electron microscopy. Western blot analysis showed that the major filament components were cross-reacted with monoclonal antibodies against animal keratin. The phenomenon was in concert with the result of indirect immunofluoreseenee observation. The filaments with 10 nm in diameter could be reassembled in vitro. Using selective extraction, proteins were prepared from cells of Spirulina subtillissima Kutz., thalli of Marchantia polymorpha L., and leaf blades of A. philippense L. , Ginkgo biloba L. and Brassica pekinensis Rupr. Western blot showed that S. subtillissima Kutz. has two acidic keratin-like pro- teins and all of the other four plant species have three basic keratin-like proteins and three acidic keratin-like proteins. These results may suggest the existance of an intermediate filament network with keratin-like proteins in the cells of pteridophyte and their existance in plant cells is popular.