Monoclonal antibodies have been raised against N- and C-terminal desmin sequence regions. 2. The antibodies decorated desmin intermediate filaments in a helical fashion with four antibody molecules per helix turn. 3. The filaments could be decorated with both types of antibody consecutively. 4. These results support a model of intermediate filament assembly in which the tetrameric protofilaments are aligned in a staggered fashion with partial overlapping of the central rod domain regions of the desmin sequence.